Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.85   9.275%   $68.6793   $68.68   $68.70   $68.70  
  Purchase #2 $229.66   7.343%   $246.5239   $246.52   $246.50   $246.50  
  Purchase #3 $122.54   4.146%   $127.6205   $127.62   $127.60   $127.60  
  Purchase #4 $164.33   11.221%   $182.7695   $182.77   $182.75   $182.80  
  Purchase #5 $127.62   8.218%   $138.1078   $138.11   $138.10   $138.10  
  Purchase #6 $184.93   4.551%   $193.3462   $193.35   $193.35   $193.30  
  Purchase #7 $116.66   10.354%   $128.739   $128.74   $128.75   $128.70  
  7 purchase totals = $1,008.59       $1,085.7862   $1,085.79   $1,085.75   $1,085.70