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 $96.57   9.710%   $105.9469   $105.95   $105.95   $105.90  
  Purchase #2 $194.35   9.576%   $212.961   $212.96   $212.95   $213.00  
  Purchase #3 $105.86   4.541%   $110.6671   $110.67   $110.65   $110.70  
  Purchase #4 $84.64   13.727%   $96.2585   $96.26   $96.25   $96.30  
  Purchase #5 $12.97   10.381%   $14.3164   $14.32   $14.30   $14.30  
  Purchase #6 $120.34   12.650%   $135.563   $135.56   $135.55   $135.60  
  Purchase #7 $209.30   12.629%   $235.7325   $235.73   $235.75   $235.70  
  7 purchase totals = $824.03       $911.4454   $911.45   $911.40   $911.50