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 $62.33   11.772%   $69.6675   $69.67   $69.65   $69.70  
  Purchase #2 $118.32   13.165%   $133.8968   $133.90   $133.90   $133.90  
  Purchase #3 $138.82   8.475%   $150.585   $150.59   $150.60   $150.60  
  Purchase #4 $182.97   13.527%   $207.7204   $207.72   $207.70   $207.70  
  Purchase #5 $169.79   10.316%   $187.3055   $187.31   $187.30   $187.30  
  Purchase #6 $129.38   11.672%   $144.4812   $144.48   $144.50   $144.50  
  Purchase #7 $234.36   8.450%   $254.1634   $254.16   $254.15   $254.20  
  7 purchase totals = $1,035.97       $1,147.8198   $1,147.83   $1,147.80   $1,147.90