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 $72.79   3.848%   $75.591   $75.59   $75.60   $75.60  
  Purchase #2 $211.38   3.652%   $219.0996   $219.10   $219.10   $219.10  
  Purchase #3 $23.44   5.625%   $24.7585   $24.76   $24.75   $24.80  
  Purchase #4 $149.57   8.785%   $162.7097   $162.71   $162.70   $162.70  
  Purchase #5 $87.45   10.126%   $96.3052   $96.31   $96.30   $96.30  
  Purchase #6 $210.99   5.242%   $222.0501   $222.05   $222.05   $222.10  
  Purchase #7 $227.64   13.201%   $257.6908   $257.69   $257.70   $257.70  
  7 purchase totals = $983.26       $1,058.2049   $1,058.21   $1,058.20   $1,058.30