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 $46.94   3.439%   $48.5543   $48.55   $48.55   $48.60  
  Purchase #2 $192.75   13.114%   $218.0272   $218.03   $218.05   $218.00  
  Purchase #3 $83.42   12.658%   $93.9793   $93.98   $94.00   $94.00  
  Purchase #4 $232.78   3.847%   $241.735   $241.74   $241.75   $241.70  
  Purchase #5 $172.57   11.293%   $192.0583   $192.06   $192.05   $192.10  
  Purchase #6 $126.67   8.119%   $136.9543   $136.95   $136.95   $137.00  
  Purchase #7 $82.79   9.293%   $90.4837   $90.48   $90.50   $90.50  
  7 purchase totals = $937.92       $1,021.7921   $1,021.79   $1,021.85   $1,021.90