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 $54.42   13.278%   $61.6459   $61.65   $61.65   $61.60  
  Purchase #2 $186.84   13.425%   $211.9233   $211.92   $211.90   $211.90  
  Purchase #3 $61.36   4.633%   $64.2028   $64.20   $64.20   $64.20  
  Purchase #4 $152.48   8.469%   $165.3935   $165.39   $165.40   $165.40  
  Purchase #5 $235.96   10.309%   $260.2851   $260.29   $260.30   $260.30  
  Purchase #6 $124.87   7.297%   $133.9818   $133.98   $134.00   $134.00  
  Purchase #7 $201.88   13.634%   $229.4043   $229.40   $229.40   $229.40  
  7 purchase totals = $1,017.81       $1,126.8367   $1,126.83   $1,126.85   $1,126.80