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 $228.56   5.601%   $241.3616   $241.36   $241.35   $241.40  
  Purchase #2 $208.83   4.764%   $218.7787   $218.78   $218.80   $218.80  
  Purchase #3 $16.43   9.785%   $18.0377   $18.04   $18.05   $18.00  
  Purchase #4 $218.90   11.424%   $243.9071   $243.91   $243.90   $243.90  
  Purchase #5 $134.29   11.711%   $150.0167   $150.02   $150.00   $150.00  
  Purchase #6 $48.59   12.273%   $54.5535   $54.55   $54.55   $54.60  
  Purchase #7 $220.26   13.288%   $249.5281   $249.53   $249.55   $249.50  
  7 purchase totals = $1,075.86       $1,176.1834   $1,176.19   $1,176.20   $1,176.20