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 $191.84   7.358%   $205.9556   $205.96   $205.95   $206.00  
  Purchase #2 $206.32   5.132%   $216.9083   $216.91   $216.90   $216.90  
  Purchase #3 $88.92   13.583%   $100.998   $101.00   $101.00   $101.00  
  Purchase #4 $139.52   7.624%   $150.157   $150.16   $150.15   $150.20  
  Purchase #5 $36.90   6.162%   $39.1738   $39.17   $39.15   $39.20  
  Purchase #6 $23.90   11.516%   $26.6523   $26.65   $26.65   $26.70  
  Purchase #7 $175.28   7.310%   $188.093   $188.09   $188.10   $188.10  
  7 purchase totals = $862.68       $927.9380   $927.94   $927.90   $928.10