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 $126.39   5.272%   $133.0533   $133.05   $133.05   $133.10  
  Purchase #2 $79.73   7.277%   $85.532   $85.53   $85.55   $85.50  
  Purchase #3 $38.71   6.331%   $41.1607   $41.16   $41.15   $41.20  
  Purchase #4 $83.50   5.424%   $88.029   $88.03   $88.05   $88.00  
  Purchase #5 $45.51   9.149%   $49.6737   $49.67   $49.65   $49.70  
  Purchase #6 $213.71   8.819%   $232.5571   $232.56   $232.55   $232.60  
  Purchase #7 $48.76   8.454%   $52.8822   $52.88   $52.90   $52.90  
  7 purchase totals = $636.31       $682.8880   $682.88   $682.90   $683.00