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 $92.70   4.157%   $96.5535   $96.55   $96.55   $96.60  
  Purchase #2 $82.69   11.174%   $91.9298   $91.93   $91.95   $91.90  
  Purchase #3 $159.27   7.308%   $170.9095   $170.91   $170.90   $170.90  
  Purchase #4 $35.31   9.374%   $38.62   $38.62   $38.60   $38.60  
  Purchase #5 $16.76   5.502%   $17.6821   $17.68   $17.70   $17.70  
  Purchase #6 $211.86   6.570%   $225.7792   $225.78   $225.80   $225.80  
  Purchase #7 $75.37   13.201%   $85.3196   $85.32   $85.30   $85.30  
  7 purchase totals = $673.96       $726.7937   $726.79   $726.80   $726.80