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 $91.98   9.421%   $100.6454   $100.65   $100.65   $100.60  
  Purchase #2 $59.66   10.579%   $65.9714   $65.97   $65.95   $66.00  
  Purchase #3 $76.98   6.764%   $82.1869   $82.19   $82.20   $82.20  
  Purchase #4 $181.81   10.544%   $200.98   $200.98   $201.00   $201.00  
  Purchase #5 $155.68   9.538%   $170.5288   $170.53   $170.55   $170.50  
  Purchase #6 $228.98   11.677%   $255.718   $255.72   $255.70   $255.70  
  Purchase #7 $139.54   8.492%   $151.3897   $151.39   $151.40   $151.40  
  7 purchase totals = $934.63       $1,027.4202   $1,027.43   $1,027.45   $1,027.40