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 $64.57   8.396%   $69.9913   $69.99   $70.00   $70.00  
  Purchase #2 $64.28   13.731%   $73.1063   $73.11   $73.10   $73.10  
  Purchase #3 $191.83   13.573%   $217.8671   $217.87   $217.85   $217.90  
  Purchase #4 $5.32   8.170%   $5.7546   $5.75   $5.75   $5.80  
  Purchase #5 $243.49   12.371%   $273.6121   $273.61   $273.60   $273.60  
  Purchase #6 $211.25   11.344%   $235.2142   $235.21   $235.20   $235.20  
  Purchase #7 $62.33   10.583%   $68.9264   $68.93   $68.95   $68.90  
  7 purchase totals = $843.07       $944.4720   $944.47   $944.45   $944.50