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 $92.94   6.212%   $98.7134   $98.71   $98.70   $98.70  
  Purchase #2 $246.93   13.607%   $280.5298   $280.53   $280.55   $280.50  
  Purchase #3 $108.68   7.489%   $116.819   $116.82   $116.80   $116.80  
  Purchase #4 $232.62   9.744%   $255.2865   $255.29   $255.30   $255.30  
  Purchase #5 $241.80   8.803%   $263.0857   $263.09   $263.10   $263.10  
  Purchase #6 $174.45   11.349%   $194.2483   $194.25   $194.25   $194.20  
  Purchase #7 $138.84   9.464%   $151.9798   $151.98   $152.00   $152.00  
  7 purchase totals = $1,236.26       $1,360.6625   $1,360.67   $1,360.70   $1,360.60