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 $94.89   3.628%   $98.3326   $98.33   $98.35   $98.30  
  Purchase #2 $85.25   11.828%   $95.3334   $95.33   $95.35   $95.30  
  Purchase #3 $245.75   10.578%   $271.7454   $271.75   $271.75   $271.70  
  Purchase #4 $31.57   4.472%   $32.9818   $32.98   $33.00   $33.00  
  Purchase #5 $200.91   9.225%   $219.4439   $219.44   $219.45   $219.40  
  Purchase #6 $154.73   4.869%   $162.2638   $162.26   $162.25   $162.30  
  Purchase #7 $149.81   9.150%   $163.5176   $163.52   $163.50   $163.50  
  7 purchase totals = $962.91       $1,043.6185   $1,043.61   $1,043.65   $1,043.50