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 $64.33   3.228%   $66.4066   $66.41   $66.40   $66.40  
  Purchase #2 $155.50   11.448%   $173.3016   $173.30   $173.30   $173.30  
  Purchase #3 $189.36   6.721%   $202.0869   $202.09   $202.10   $202.10  
  Purchase #4 $191.42   5.834%   $202.5874   $202.59   $202.60   $202.60  
  Purchase #5 $12.76   9.402%   $13.9597   $13.96   $13.95   $14.00  
  Purchase #6 $39.76   12.463%   $44.7153   $44.72   $44.70   $44.70  
  Purchase #7 $44.84   4.398%   $46.8121   $46.81   $46.80   $46.80  
  7 purchase totals = $697.97       $749.8696   $749.88   $749.85   $749.90