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 $225.89   7.461%   $242.7437   $242.74   $242.75   $242.70  
  Purchase #2 $95.85   11.379%   $106.7568   $106.76   $106.75   $106.80  
  Purchase #3 $58.90   5.520%   $62.1513   $62.15   $62.15   $62.20  
  Purchase #4 $113.47   8.158%   $122.7269   $122.73   $122.75   $122.70  
  Purchase #5 $8.72   6.706%   $9.3048   $9.30   $9.30   $9.30  
  Purchase #6 $106.50   13.626%   $121.0117   $121.01   $121.00   $121.00  
  Purchase #7 $110.72   9.264%   $120.9771   $120.98   $121.00   $121.00  
  7 purchase totals = $720.05       $785.6723   $785.67   $785.70   $785.70