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 $53.80   11.221%   $59.8369   $59.84   $59.85   $59.80  
  Purchase #2 $110.64   7.170%   $118.5729   $118.57   $118.55   $118.60  
  Purchase #3 $123.99   7.589%   $133.3996   $133.40   $133.40   $133.40  
  Purchase #4 $234.56   5.199%   $246.7548   $246.75   $246.75   $246.80  
  Purchase #5 $61.80   6.492%   $65.8121   $65.81   $65.80   $65.80  
  Purchase #6 $219.44   9.449%   $240.1749   $240.17   $240.15   $240.20  
  Purchase #7 $11.91   3.494%   $12.3261   $12.33   $12.35   $12.30  
  7 purchase totals = $816.14       $876.8773   $876.87   $876.85   $876.90