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 $209.50   11.330%   $233.2364   $233.24   $233.25   $233.20  
  Purchase #2 $21.74   4.213%   $22.6559   $22.66   $22.65   $22.70  
  Purchase #3 $219.64   6.614%   $234.167   $234.17   $234.15   $234.20  
  Purchase #4 $247.65   6.361%   $263.403   $263.40   $263.40   $263.40  
  Purchase #5 $205.70   3.226%   $212.3359   $212.34   $212.35   $212.30  
  Purchase #6 $100.30   12.413%   $112.7502   $112.75   $112.75   $112.80  
  Purchase #7 $119.83   4.279%   $124.9575   $124.96   $124.95   $125.00  
  7 purchase totals = $1,124.36       $1,203.5059   $1,203.52   $1,203.50   $1,203.60