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 $88.55   9.230%   $96.7232   $96.72   $96.70   $96.70  
  Purchase #2 $162.77   13.424%   $184.6202   $184.62   $184.60   $184.60  
  Purchase #3 $31.35   4.202%   $32.6673   $32.67   $32.65   $32.70  
  Purchase #4 $75.64   7.370%   $81.2147   $81.21   $81.20   $81.20  
  Purchase #5 $201.42   13.165%   $227.9369   $227.94   $227.95   $227.90  
  Purchase #6 $184.92   4.607%   $193.4393   $193.44   $193.45   $193.40  
  Purchase #7 $209.44   5.520%   $221.0011   $221.00   $221.00   $221.00  
  7 purchase totals = $954.09       $1,037.6027   $1,037.60   $1,037.55   $1,037.50