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 $51.70   11.259%   $57.5209   $57.52   $57.50   $57.50  
  Purchase #2 $151.88   3.814%   $157.6727   $157.67   $157.65   $157.70  
  Purchase #3 $177.39   8.281%   $192.0797   $192.08   $192.10   $192.10  
  Purchase #4 $134.51   9.245%   $146.9454   $146.95   $146.95   $146.90  
  Purchase #5 $209.84   12.485%   $236.0385   $236.04   $236.05   $236.00  
  Purchase #6 $72.50   4.769%   $75.9575   $75.96   $75.95   $76.00  
  Purchase #7 $228.60   9.486%   $250.285   $250.29   $250.30   $250.30  
  7 purchase totals = $1,026.42       $1,116.4997   $1,116.51   $1,116.50   $1,116.50