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 $117.61   12.209%   $131.969   $131.97   $131.95   $132.00  
  Purchase #2 $180.67   7.840%   $194.8345   $194.83   $194.85   $194.80  
  Purchase #3 $179.85   7.599%   $193.5168   $193.52   $193.50   $193.50  
  Purchase #4 $56.96   7.506%   $61.2354   $61.24   $61.25   $61.20  
  Purchase #5 $116.41   13.572%   $132.2092   $132.21   $132.20   $132.20  
  Purchase #6 $231.29   6.507%   $246.34   $246.34   $246.35   $246.30  
  Purchase #7 $87.47   10.843%   $96.9544   $96.95   $96.95   $97.00  
  7 purchase totals = $970.26       $1,057.0593   $1,057.06   $1,057.05   $1,057.00