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 $204.68   8.219%   $221.5026   $221.50   $221.50   $221.50  
  Purchase #2 $96.46   8.589%   $104.7449   $104.74   $104.75   $104.70  
  Purchase #3 $10.31   10.774%   $11.4208   $11.42   $11.40   $11.40  
  Purchase #4 $118.43   7.722%   $127.5752   $127.58   $127.60   $127.60  
  Purchase #5 $165.84   10.807%   $183.7623   $183.76   $183.75   $183.80  
  Purchase #6 $23.80   4.278%   $24.8182   $24.82   $24.80   $24.80  
  Purchase #7 $241.91   6.780%   $258.3115   $258.31   $258.30   $258.30  
  7 purchase totals = $861.43       $932.1355   $932.13   $932.10   $932.10