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 $191.96   7.615%   $206.5778   $206.58   $206.60   $206.60  
  Purchase #2 $73.74   13.263%   $83.5201   $83.52   $83.50   $83.50  
  Purchase #3 $6.84   3.559%   $7.0834   $7.08   $7.10   $7.10  
  Purchase #4 $106.73   3.198%   $110.1432   $110.14   $110.15   $110.10  
  Purchase #5 $49.91   7.377%   $53.5919   $53.59   $53.60   $53.60  
  Purchase #6 $249.99   11.505%   $278.7513   $278.75   $278.75   $278.80  
  Purchase #7 $247.51   5.284%   $260.5884   $260.59   $260.60   $260.60  
  7 purchase totals = $926.68       $1,000.2561   $1,000.25   $1,000.30   $1,000.30