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 $93.91   5.468%   $99.045   $99.05   $99.05   $99.00  
  Purchase #2 $6.85   7.270%   $7.348   $7.35   $7.35   $7.30  
  Purchase #3 $235.37   5.821%   $249.0709   $249.07   $249.05   $249.10  
  Purchase #4 $70.75   4.309%   $73.7986   $73.80   $73.80   $73.80  
  Purchase #5 $212.34   9.742%   $233.0262   $233.03   $233.05   $233.00  
  Purchase #6 $71.59   13.390%   $81.1759   $81.18   $81.20   $81.20  
  Purchase #7 $118.95   10.809%   $131.8073   $131.81   $131.80   $131.80  
  7 purchase totals = $809.76       $875.2719   $875.29   $875.30   $875.20