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 $180.68   11.780%   $201.9641   $201.96   $201.95   $202.00  
  Purchase #2 $224.26   7.205%   $240.4179   $240.42   $240.40   $240.40  
  Purchase #3 $60.35   3.256%   $62.315   $62.32   $62.30   $62.30  
  Purchase #4 $159.37   9.848%   $175.0648   $175.06   $175.05   $175.10  
  Purchase #5 $110.40   11.739%   $123.3599   $123.36   $123.35   $123.40  
  Purchase #6 $94.29   8.112%   $101.9388   $101.94   $101.95   $101.90  
  Purchase #7 $101.66   11.417%   $113.2665   $113.27   $113.25   $113.30  
  7 purchase totals = $931.01       $1,018.3270   $1,018.33   $1,018.25   $1,018.40