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 $208.95   8.753%   $227.2394   $227.24   $227.25   $227.20  
  Purchase #2 $49.45   6.759%   $52.7923   $52.79   $52.80   $52.80  
  Purchase #3 $240.62   9.465%   $263.3947   $263.39   $263.40   $263.40  
  Purchase #4 $151.85   6.669%   $161.9769   $161.98   $162.00   $162.00  
  Purchase #5 $47.50   5.585%   $50.1529   $50.15   $50.15   $50.20  
  Purchase #6 $93.37   8.402%   $101.2149   $101.21   $101.20   $101.20  
  Purchase #7 $179.35   6.556%   $191.1082   $191.11   $191.10   $191.10  
  7 purchase totals = $971.09       $1,047.8793   $1,047.87   $1,047.90   $1,047.90