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 $116.97   3.210%   $120.7247   $120.72   $120.70   $120.70  
  Purchase #2 $13.86   3.353%   $14.3247   $14.32   $14.30   $14.30  
  Purchase #3 $149.90   10.522%   $165.6725   $165.67   $165.65   $165.70  
  Purchase #4 $71.63   5.821%   $75.7996   $75.80   $75.80   $75.80  
  Purchase #5 $59.97   11.565%   $66.9055   $66.91   $66.90   $66.90  
  Purchase #6 $54.67   3.197%   $56.4178   $56.42   $56.40   $56.40  
  Purchase #7 $88.56   8.304%   $95.914   $95.91   $95.90   $95.90  
  7 purchase totals = $555.56       $595.7588   $595.75   $595.65   $595.70