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 $6.95   11.591%   $7.7556   $7.76   $7.75   $7.80  
  Purchase #2 $209.44   11.514%   $233.5549   $233.55   $233.55   $233.60  
  Purchase #3 $86.97   9.204%   $94.9747   $94.97   $94.95   $95.00  
  Purchase #4 $234.68   10.826%   $260.0865   $260.09   $260.10   $260.10  
  Purchase #5 $151.52   5.460%   $159.793   $159.79   $159.80   $159.80  
  Purchase #6 $51.75   5.820%   $54.7619   $54.76   $54.75   $54.80  
  Purchase #7 $24.75   6.797%   $26.4323   $26.43   $26.45   $26.40  
  7 purchase totals = $766.06       $837.3589   $837.35   $837.35   $837.50