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 $184.74   10.827%   $204.7418   $204.74   $204.75   $204.70  
  Purchase #2 $120.95   8.278%   $130.9622   $130.96   $130.95   $131.00  
  Purchase #3 $236.37   8.615%   $256.7333   $256.73   $256.75   $256.70  
  Purchase #4 $223.91   3.833%   $232.4925   $232.49   $232.50   $232.50  
  Purchase #5 $211.95   11.824%   $237.011   $237.01   $237.00   $237.00  
  Purchase #6 $208.78   10.518%   $230.7395   $230.74   $230.75   $230.70  
  Purchase #7 $45.25   11.587%   $50.4931   $50.49   $50.50   $50.50  
  7 purchase totals = $1,231.95       $1,343.1734   $1,343.16   $1,343.20   $1,343.10