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 $147.30   6.206%   $156.4414   $156.44   $156.45   $156.40  
  Purchase #2 $205.82   13.169%   $232.9244   $232.92   $232.90   $232.90  
  Purchase #3 $192.42   9.136%   $209.9995   $210.00   $210.00   $210.00  
  Purchase #4 $58.59   7.188%   $62.8014   $62.80   $62.80   $62.80  
  Purchase #5 $156.71   13.711%   $178.1965   $178.20   $178.20   $178.20  
  Purchase #6 $138.89   10.232%   $153.1012   $153.10   $153.10   $153.10  
  Purchase #7 $169.51   13.798%   $192.899   $192.90   $192.90   $192.90  
  7 purchase totals = $1,069.24       $1,186.3634   $1,186.36   $1,186.35   $1,186.30