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 $38.70   12.268%   $43.4477   $43.45   $43.45   $43.40  
  Purchase #2 $202.94   6.524%   $216.1798   $216.18   $216.20   $216.20  
  Purchase #3 $141.68   12.224%   $158.999   $159.00   $159.00   $159.00  
  Purchase #4 $181.60   8.279%   $196.6347   $196.63   $196.65   $196.60  
  Purchase #5 $126.37   4.696%   $132.3043   $132.30   $132.30   $132.30  
  Purchase #6 $97.92   6.221%   $104.0116   $104.01   $104.00   $104.00  
  Purchase #7 $24.72   3.238%   $25.5204   $25.52   $25.50   $25.50  
  7 purchase totals = $813.93       $877.0975   $877.09   $877.10   $877.00