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 $141.45   8.127%   $152.9456   $152.95   $152.95   $152.90  
  Purchase #2 $109.55   13.378%   $124.2056   $124.21   $124.20   $124.20  
  Purchase #3 $116.48   7.814%   $125.5817   $125.58   $125.60   $125.60  
  Purchase #4 $59.65   7.478%   $64.1106   $64.11   $64.10   $64.10  
  Purchase #5 $208.69   12.673%   $235.1373   $235.14   $235.15   $235.10  
  Purchase #6 $49.63   5.298%   $52.2594   $52.26   $52.25   $52.30  
  Purchase #7 $91.69   13.489%   $104.0581   $104.06   $104.05   $104.10  
  7 purchase totals = $777.14       $858.2983   $858.31   $858.30   $858.30