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 $151.96   11.674%   $169.6998   $169.70   $169.70   $169.70  
  Purchase #2 $163.60   4.110%   $170.324   $170.32   $170.30   $170.30  
  Purchase #3 $23.98   12.640%   $27.0111   $27.01   $27.00   $27.00  
  Purchase #4 $152.78   5.496%   $161.1768   $161.18   $161.20   $161.20  
  Purchase #5 $218.92   7.261%   $234.8158   $234.82   $234.80   $234.80  
  Purchase #6 $81.82   10.866%   $90.7106   $90.71   $90.70   $90.70  
  Purchase #7 $196.79   5.133%   $206.8912   $206.89   $206.90   $206.90  
  7 purchase totals = $989.85       $1,060.6293   $1,060.63   $1,060.60   $1,060.60