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 $189.53   9.244%   $207.0502   $207.05   $207.05   $207.10  
  Purchase #2 $52.94   10.176%   $58.3272   $58.33   $58.35   $58.30  
  Purchase #3 $229.58   9.293%   $250.9149   $250.91   $250.90   $250.90  
  Purchase #4 $132.29   13.511%   $150.1637   $150.16   $150.15   $150.20  
  Purchase #5 $169.66   7.670%   $182.6729   $182.67   $182.65   $182.70  
  Purchase #6 $162.49   11.519%   $181.2072   $181.21   $181.20   $181.20  
  Purchase #7 $187.44   4.761%   $196.364   $196.36   $196.35   $196.40  
  7 purchase totals = $1,123.93       $1,226.7001   $1,226.69   $1,226.65   $1,226.80