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 $95.75   13.779%   $108.9434   $108.94   $108.95   $108.90  
  Purchase #2 $149.95   11.175%   $166.7069   $166.71   $166.70   $166.70  
  Purchase #3 $29.33   3.529%   $30.3651   $30.37   $30.35   $30.40  
  Purchase #4 $140.73   9.207%   $153.687   $153.69   $153.70   $153.70  
  Purchase #5 $41.36   6.234%   $43.9384   $43.94   $43.95   $43.90  
  Purchase #6 $144.77   7.153%   $155.1254   $155.13   $155.15   $155.10  
  Purchase #7 $101.60   11.281%   $113.0615   $113.06   $113.05   $113.10  
  7 purchase totals = $703.49       $771.8277   $771.84   $771.85   $771.80