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 $61.79   10.805%   $68.4664   $68.47   $68.45   $68.50  
  Purchase #2 $174.51   8.609%   $189.5336   $189.53   $189.55   $189.50  
  Purchase #3 $136.71   5.864%   $144.7267   $144.73   $144.75   $144.70  
  Purchase #4 $72.66   4.124%   $75.6565   $75.66   $75.65   $75.70  
  Purchase #5 $31.30   6.117%   $33.2146   $33.21   $33.20   $33.20  
  Purchase #6 $212.98   5.228%   $224.1146   $224.11   $224.10   $224.10  
  Purchase #7 $81.39   11.207%   $90.5114   $90.51   $90.50   $90.50  
  7 purchase totals = $771.34       $826.2238   $826.22   $826.20   $826.20