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 $69.27   8.147%   $74.9134   $74.91   $74.90   $74.90  
  Purchase #2 $26.30   6.847%   $28.1008   $28.10   $28.10   $28.10  
  Purchase #3 $205.92   11.522%   $229.6461   $229.65   $229.65   $229.60  
  Purchase #4 $139.61   5.468%   $147.2439   $147.24   $147.25   $147.20  
  Purchase #5 $50.65   6.644%   $54.0152   $54.02   $54.00   $54.00  
  Purchase #6 $102.29   9.528%   $112.0362   $112.04   $112.05   $112.00  
  Purchase #7 $73.74   9.805%   $80.9702   $80.97   $80.95   $81.00  
  7 purchase totals = $667.78       $726.9258   $726.93   $726.90   $726.80