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 $129.33   10.728%   $143.2045   $143.20   $143.20   $143.20  
  Purchase #2 $212.79   13.460%   $241.4315   $241.43   $241.45   $241.40  
  Purchase #3 $92.29   4.319%   $96.276   $96.28   $96.30   $96.30  
  Purchase #4 $51.92   12.404%   $58.3602   $58.36   $58.35   $58.40  
  Purchase #5 $105.74   12.701%   $119.17   $119.17   $119.15   $119.20  
  Purchase #6 $191.31   6.484%   $203.7145   $203.71   $203.70   $203.70  
  Purchase #7 $144.70   11.421%   $161.2262   $161.23   $161.25   $161.20  
  7 purchase totals = $928.08       $1,023.3829   $1,023.38   $1,023.40   $1,023.40