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 $218.42   10.642%   $241.6643   $241.66   $241.65   $241.70  
  Purchase #2 $22.52   7.129%   $24.1255   $24.13   $24.15   $24.10  
  Purchase #3 $126.73   11.843%   $141.7386   $141.74   $141.75   $141.70  
  Purchase #4 $162.35   11.568%   $181.1306   $181.13   $181.15   $181.10  
  Purchase #5 $80.82   6.271%   $85.8882   $85.89   $85.90   $85.90  
  Purchase #6 $11.65   8.810%   $12.6764   $12.68   $12.70   $12.70  
  Purchase #7 $236.70   8.581%   $257.0112   $257.01   $257.00   $257.00  
  7 purchase totals = $859.19       $944.2348   $944.24   $944.30   $944.20