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 $82.72   12.463%   $93.0294   $93.03   $93.05   $93.00  
  Purchase #2 $147.71   6.181%   $156.84   $156.84   $156.85   $156.80  
  Purchase #3 $76.55   7.338%   $82.1672   $82.17   $82.15   $82.20  
  Purchase #4 $193.71   8.514%   $210.2025   $210.20   $210.20   $210.20  
  Purchase #5 $245.59   8.188%   $265.6989   $265.70   $265.70   $265.70  
  Purchase #6 $202.58   3.804%   $210.2861   $210.29   $210.30   $210.30  
  Purchase #7 $199.71   9.454%   $218.5906   $218.59   $218.60   $218.60  
  7 purchase totals = $1,148.57       $1,236.8147   $1,236.82   $1,236.85   $1,236.80