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 $84.66   10.646%   $93.6729   $93.67   $93.65   $93.70  
  Purchase #2 $69.59   12.694%   $78.4238   $78.42   $78.40   $78.40  
  Purchase #3 $210.35   9.558%   $230.4553   $230.46   $230.45   $230.50  
  Purchase #4 $174.87   10.840%   $193.8259   $193.83   $193.85   $193.80  
  Purchase #5 $112.60   10.551%   $124.4804   $124.48   $124.50   $124.50  
  Purchase #6 $224.84   4.392%   $234.715   $234.72   $234.70   $234.70  
  Purchase #7 $95.30   3.131%   $98.2838   $98.28   $98.30   $98.30  
  7 purchase totals = $972.21       $1,053.8571   $1,053.86   $1,053.85   $1,053.90