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 $73.50   4.823%   $77.0449   $77.04   $77.05   $77.00  
  Purchase #2 $164.78   13.232%   $186.5837   $186.58   $186.60   $186.60  
  Purchase #3 $87.46   5.310%   $92.1041   $92.10   $92.10   $92.10  
  Purchase #4 $78.96   3.626%   $81.8231   $81.82   $81.80   $81.80  
  Purchase #5 $242.67   12.371%   $272.6907   $272.69   $272.70   $272.70  
  Purchase #6 $126.30   5.164%   $132.8221   $132.82   $132.80   $132.80  
  Purchase #7 $52.89   9.702%   $58.0214   $58.02   $58.00   $58.00  
  7 purchase totals = $826.56       $901.0900   $901.07   $901.05   $901.00