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 $167.39   8.310%   $181.3001   $181.30   $181.30   $181.30  
  Purchase #2 $131.89   9.153%   $143.9619   $143.96   $143.95   $144.00  
  Purchase #3 $66.41   12.874%   $74.9596   $74.96   $74.95   $75.00  
  Purchase #4 $27.27   5.167%   $28.679   $28.68   $28.70   $28.70  
  Purchase #5 $220.65   11.571%   $246.1814   $246.18   $246.20   $246.20  
  Purchase #6 $128.29   8.516%   $139.2152   $139.22   $139.20   $139.20  
  Purchase #7 $41.33   10.495%   $45.6676   $45.67   $45.65   $45.70  
  7 purchase totals = $783.23       $859.9648   $859.97   $859.95   $860.10