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 $54.55   8.628%   $59.2566   $59.26   $59.25   $59.30  
  Purchase #2 $131.53   7.213%   $141.0173   $141.02   $141.00   $141.00  
  Purchase #3 $239.95   13.681%   $272.7776   $272.78   $272.80   $272.80  
  Purchase #4 $211.56   9.796%   $232.2844   $232.28   $232.30   $232.30  
  Purchase #5 $137.74   7.380%   $147.9052   $147.91   $147.90   $147.90  
  Purchase #6 $155.42   11.550%   $173.371   $173.37   $173.35   $173.40  
  Purchase #7 $192.43   9.304%   $210.3337   $210.33   $210.35   $210.30  
  7 purchase totals = $1,123.18       $1,236.9458   $1,236.95   $1,236.95   $1,237.00