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 $208.52   8.126%   $225.4643   $225.46   $225.45   $225.50  
  Purchase #2 $176.49   10.107%   $194.3278   $194.33   $194.35   $194.30  
  Purchase #3 $228.57   11.774%   $255.4818   $255.48   $255.50   $255.50  
  Purchase #4 $202.39   5.445%   $213.4101   $213.41   $213.40   $213.40  
  Purchase #5 $227.62   9.345%   $248.8911   $248.89   $248.90   $248.90  
  Purchase #6 $92.50   13.737%   $105.2067   $105.21   $105.20   $105.20  
  Purchase #7 $96.90   11.500%   $108.0435   $108.04   $108.05   $108.00  
  7 purchase totals = $1,232.99       $1,350.8253   $1,350.82   $1,350.85   $1,350.80