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 $62.94   11.707%   $70.3084   $70.31   $70.30   $70.30  
  Purchase #2 $149.63   8.682%   $162.6209   $162.62   $162.60   $162.60  
  Purchase #3 $26.60   9.233%   $29.056   $29.06   $29.05   $29.10  
  Purchase #4 $203.36   3.436%   $210.3474   $210.35   $210.35   $210.30  
  Purchase #5 $221.35   7.474%   $237.8937   $237.89   $237.90   $237.90  
  Purchase #6 $180.89   11.236%   $201.2148   $201.21   $201.20   $201.20  
  Purchase #7 $220.75   6.794%   $235.7478   $235.75   $235.75   $235.70  
  7 purchase totals = $1,065.52       $1,147.1890   $1,147.19   $1,147.15   $1,147.10