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 $215.76   12.148%   $241.9705   $241.97   $241.95   $242.00  
  Purchase #2 $226.68   6.304%   $240.9699   $240.97   $240.95   $241.00  
  Purchase #3 $141.52   6.542%   $150.7782   $150.78   $150.80   $150.80  
  Purchase #4 $126.73   10.501%   $140.0379   $140.04   $140.05   $140.00  
  Purchase #5 $13.72   11.672%   $15.3214   $15.32   $15.30   $15.30  
  Purchase #6 $24.33   7.760%   $26.218   $26.22   $26.20   $26.20  
  Purchase #7 $209.45   7.804%   $225.7955   $225.80   $225.80   $225.80  
  7 purchase totals = $958.19       $1,041.0914   $1,041.10   $1,041.05   $1,041.10