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 $86.59   8.721%   $94.1415   $94.14   $94.15   $94.10  
  Purchase #2 $130.98   6.125%   $139.0025   $139.00   $139.00   $139.00  
  Purchase #3 $247.85   8.391%   $268.6471   $268.65   $268.65   $268.60  
  Purchase #4 $209.78   11.489%   $233.8816   $233.88   $233.90   $233.90  
  Purchase #5 $152.76   9.469%   $167.2248   $167.22   $167.20   $167.20  
  Purchase #6 $153.45   11.785%   $171.5341   $171.53   $171.55   $171.50  
  Purchase #7 $138.99   5.572%   $146.7345   $146.73   $146.75   $146.70  
  7 purchase totals = $1,120.40       $1,221.1661   $1,221.15   $1,221.20   $1,221.00