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 $211.64   9.648%   $232.059   $232.06   $232.05   $232.10  
  Purchase #2 $148.59   13.547%   $168.7195   $168.72   $168.70   $168.70  
  Purchase #3 $138.49   11.806%   $154.8401   $154.84   $154.85   $154.80  
  Purchase #4 $123.53   11.483%   $137.7149   $137.71   $137.70   $137.70  
  Purchase #5 $214.83   11.842%   $240.2702   $240.27   $240.25   $240.30  
  Purchase #6 $109.34   13.264%   $123.8429   $123.84   $123.85   $123.80  
  Purchase #7 $56.77   9.579%   $62.208   $62.21   $62.20   $62.20  
  7 purchase totals = $1,003.19       $1,119.6546   $1,119.65   $1,119.60   $1,119.60