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 $90.37   4.377%   $94.3255   $94.33   $94.35   $94.30  
  Purchase #2 $225.83   9.652%   $247.6271   $247.63   $247.65   $247.60  
  Purchase #3 $117.35   6.277%   $124.7161   $124.72   $124.70   $124.70  
  Purchase #4 $149.51   4.867%   $156.7867   $156.79   $156.80   $156.80  
  Purchase #5 $229.85   11.752%   $256.862   $256.86   $256.85   $256.90  
  Purchase #6 $101.54   6.545%   $108.1858   $108.19   $108.20   $108.20  
  Purchase #7 $40.74   13.272%   $46.147   $46.15   $46.15   $46.10  
  7 purchase totals = $955.19       $1,034.6502   $1,034.67   $1,034.70   $1,034.60