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 $54.88   9.774%   $60.244   $60.24   $60.25   $60.20  
  Purchase #2 $83.47   5.661%   $88.1952   $88.20   $88.20   $88.20  
  Purchase #3 $123.93   9.369%   $135.541   $135.54   $135.55   $135.50  
  Purchase #4 $14.46   8.813%   $15.7344   $15.73   $15.75   $15.70  
  Purchase #5 $69.43   7.385%   $74.5574   $74.56   $74.55   $74.60  
  Purchase #6 $211.54   7.140%   $226.644   $226.64   $226.65   $226.60  
  Purchase #7 $225.48   13.116%   $255.054   $255.05   $255.05   $255.10  
  7 purchase totals = $783.19       $855.9700   $855.96   $856.00   $855.90