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 $150.77   12.424%   $169.5017   $169.50   $169.50   $169.50  
  Purchase #2 $216.25   8.648%   $234.9513   $234.95   $234.95   $235.00  
  Purchase #3 $100.76   7.547%   $108.3644   $108.36   $108.35   $108.40  
  Purchase #4 $58.95   10.265%   $65.0012   $65.00   $65.00   $65.00  
  Purchase #5 $80.85   7.422%   $86.8507   $86.85   $86.85   $86.90  
  Purchase #6 $212.41   6.841%   $226.941   $226.94   $226.95   $226.90  
  Purchase #7 $226.55   13.499%   $257.132   $257.13   $257.15   $257.10  
  7 purchase totals = $1,046.54       $1,148.7423   $1,148.73   $1,148.75   $1,148.80