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 $191.48   10.327%   $211.2541   $211.25   $211.25   $211.30  
  Purchase #2 $185.51   11.559%   $206.9531   $206.95   $206.95   $207.00  
  Purchase #3 $48.50   11.561%   $54.1071   $54.11   $54.10   $54.10  
  Purchase #4 $246.99   10.263%   $272.3386   $272.34   $272.35   $272.30  
  Purchase #5 $83.93   9.169%   $91.6255   $91.63   $91.65   $91.60  
  Purchase #6 $12.67   6.301%   $13.4683   $13.47   $13.45   $13.50  
  Purchase #7 $157.35   6.667%   $167.8405   $167.84   $167.85   $167.80  
  7 purchase totals = $926.43       $1,017.5872   $1,017.59   $1,017.60   $1,017.60