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 $77.96   9.267%   $85.1846   $85.18   $85.20   $85.20  
  Purchase #2 $141.65   7.280%   $151.9621   $151.96   $151.95   $152.00  
  Purchase #3 $10.72   8.628%   $11.6449   $11.64   $11.65   $11.60  
  Purchase #4 $146.95   5.354%   $154.8177   $154.82   $154.80   $154.80  
  Purchase #5 $101.47   4.495%   $106.0311   $106.03   $106.05   $106.00  
  Purchase #6 $194.87   7.103%   $208.7116   $208.71   $208.70   $208.70  
  Purchase #7 $205.59   13.251%   $232.8327   $232.83   $232.85   $232.80  
  7 purchase totals = $879.21       $951.1847   $951.17   $951.20   $951.10