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 $99.95   11.706%   $111.6501   $111.65   $111.65   $111.70  
  Purchase #2 $77.42   5.334%   $81.5496   $81.55   $81.55   $81.50  
  Purchase #3 $70.80   3.316%   $73.1477   $73.15   $73.15   $73.10  
  Purchase #4 $209.37   8.221%   $226.5823   $226.58   $226.60   $226.60  
  Purchase #5 $59.57   13.324%   $67.5071   $67.51   $67.50   $67.50  
  Purchase #6 $120.84   7.354%   $129.7266   $129.73   $129.75   $129.70  
  Purchase #7 $92.46   13.589%   $105.0244   $105.02   $105.00   $105.00  
  7 purchase totals = $730.41       $795.1878   $795.19   $795.20   $795.10