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 $197.85   6.571%   $210.8507   $210.85   $210.85   $210.90  
  Purchase #2 $121.98   11.492%   $135.9979   $136.00   $136.00   $136.00  
  Purchase #3 $24.62   7.730%   $26.5231   $26.52   $26.50   $26.50  
  Purchase #4 $22.56   12.327%   $25.341   $25.34   $25.35   $25.30  
  Purchase #5 $229.70   5.271%   $241.8075   $241.81   $241.80   $241.80  
  Purchase #6 $154.33   12.563%   $173.7185   $173.72   $173.70   $173.70  
  Purchase #7 $223.29   3.840%   $231.8643   $231.86   $231.85   $231.90  
  7 purchase totals = $974.33       $1,046.1030   $1,046.10   $1,046.05   $1,046.10