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 $58.76   10.361%   $64.8481   $64.85   $64.85   $64.80  
  Purchase #2 $187.83   8.415%   $203.6359   $203.64   $203.65   $203.60  
  Purchase #3 $102.33   6.418%   $108.8975   $108.90   $108.90   $108.90  
  Purchase #4 $24.35   9.666%   $26.7037   $26.70   $26.70   $26.70  
  Purchase #5 $158.35   12.824%   $178.6568   $178.66   $178.65   $178.70  
  Purchase #6 $201.85   9.290%   $220.6019   $220.60   $220.60   $220.60  
  Purchase #7 $212.51   6.863%   $227.0946   $227.09   $227.10   $227.10  
  7 purchase totals = $945.98       $1,030.4385   $1,030.44   $1,030.45   $1,030.40