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 $100.32   6.855%   $107.1969   $107.20   $107.20   $107.20  
  Purchase #2 $17.57   11.386%   $19.5705   $19.57   $19.55   $19.60  
  Purchase #3 $124.43   9.715%   $136.5184   $136.52   $136.50   $136.50  
  Purchase #4 $213.80   13.290%   $242.214   $242.21   $242.20   $242.20  
  Purchase #5 $108.29   4.366%   $113.0179   $113.02   $113.00   $113.00  
  Purchase #6 $31.37   12.740%   $35.3665   $35.37   $35.35   $35.40  
  Purchase #7 $33.80   4.635%   $35.3666   $35.37   $35.35   $35.40  
  7 purchase totals = $629.58       $689.2508   $689.26   $689.15   $689.30