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 $205.94   13.748%   $234.2526   $234.25   $234.25   $234.30  
  Purchase #2 $65.84   5.343%   $69.3578   $69.36   $69.35   $69.40  
  Purchase #3 $24.45   11.750%   $27.3229   $27.32   $27.30   $27.30  
  Purchase #4 $107.25   6.132%   $113.8266   $113.83   $113.85   $113.80  
  Purchase #5 $37.65   9.285%   $41.1458   $41.15   $41.15   $41.10  
  Purchase #6 $202.79   8.109%   $219.2342   $219.23   $219.25   $219.20  
  Purchase #7 $113.49   11.859%   $126.9488   $126.95   $126.95   $126.90  
  7 purchase totals = $757.41       $832.0887   $832.09   $832.10   $832.00