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 $163.31   5.775%   $172.7412   $172.74   $172.75   $172.70  
  Purchase #2 $54.87   5.344%   $57.8023   $57.80   $57.80   $57.80  
  Purchase #3 $167.48   7.495%   $180.0326   $180.03   $180.05   $180.00  
  Purchase #4 $113.94   12.466%   $128.1438   $128.14   $128.15   $128.10  
  Purchase #5 $17.82   12.806%   $20.102   $20.10   $20.10   $20.10  
  Purchase #6 $201.47   6.785%   $215.1397   $215.14   $215.15   $215.10  
  Purchase #7 $121.64   8.815%   $132.3626   $132.36   $132.35   $132.40  
  7 purchase totals = $840.53       $906.3242   $906.31   $906.35   $906.20