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 $45.37   10.475%   $50.1225   $50.12   $50.10   $50.10  
  Purchase #2 $37.55   4.149%   $39.1079   $39.11   $39.10   $39.10  
  Purchase #3 $102.61   5.373%   $108.1232   $108.12   $108.10   $108.10  
  Purchase #4 $124.31   12.491%   $139.8376   $139.84   $139.85   $139.80  
  Purchase #5 $198.57   8.864%   $216.1712   $216.17   $216.15   $216.20  
  Purchase #6 $139.29   11.642%   $155.5061   $155.51   $155.50   $155.50  
  Purchase #7 $190.44   6.513%   $202.8434   $202.84   $202.85   $202.80  
  7 purchase totals = $838.14       $911.7119   $911.71   $911.65   $911.60