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 $88.82   8.464%   $96.3377   $96.34   $96.35   $96.30  
  Purchase #2 $210.77   6.292%   $224.0316   $224.03   $224.05   $224.00  
  Purchase #3 $201.68   6.567%   $214.9243   $214.92   $214.90   $214.90  
  Purchase #4 $27.67   5.287%   $29.1329   $29.13   $29.15   $29.10  
  Purchase #5 $135.27   12.251%   $151.8419   $151.84   $151.85   $151.80  
  Purchase #6 $204.87   7.766%   $220.7802   $220.78   $220.80   $220.80  
  Purchase #7 $103.74   11.717%   $115.8952   $115.90   $115.90   $115.90  
  7 purchase totals = $972.82       $1,052.9438   $1,052.94   $1,053.00   $1,052.80