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 $120.33   10.699%   $133.2041   $133.20   $133.20   $133.20  
  Purchase #2 $62.65   12.764%   $70.6466   $70.65   $70.65   $70.60  
  Purchase #3 $90.99   5.204%   $95.7251   $95.73   $95.75   $95.70  
  Purchase #4 $60.57   11.799%   $67.7167   $67.72   $67.70   $67.70  
  Purchase #5 $98.33   4.864%   $103.1128   $103.11   $103.10   $103.10  
  Purchase #6 $184.82   12.233%   $207.429   $207.43   $207.45   $207.40  
  Purchase #7 $68.78   13.480%   $78.0515   $78.05   $78.05   $78.10  
  7 purchase totals = $686.47       $755.8858   $755.89   $755.90   $755.80