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 $70.51   6.360%   $74.9944   $74.99   $75.00   $75.00  
  Purchase #2 $139.28   11.535%   $155.3459   $155.35   $155.35   $155.30  
  Purchase #3 $216.95   5.181%   $228.1902   $228.19   $228.20   $228.20  
  Purchase #4 $87.89   8.452%   $95.3185   $95.32   $95.30   $95.30  
  Purchase #5 $198.31   13.360%   $224.8042   $224.80   $224.80   $224.80  
  Purchase #6 $155.74   11.581%   $173.7762   $173.78   $173.80   $173.80  
  Purchase #7 $14.41   4.814%   $15.1037   $15.10   $15.10   $15.10  
  7 purchase totals = $883.09       $967.5331   $967.53   $967.55   $967.50