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 $98.59   9.178%   $107.6386   $107.64   $107.65   $107.60  
  Purchase #2 $242.77   8.137%   $262.5242   $262.52   $262.50   $262.50  
  Purchase #3 $51.64   13.215%   $58.4642   $58.46   $58.45   $58.50  
  Purchase #4 $245.32   6.323%   $260.8316   $260.83   $260.85   $260.80  
  Purchase #5 $39.67   9.132%   $43.2927   $43.29   $43.30   $43.30  
  Purchase #6 $138.65   12.139%   $155.4807   $155.48   $155.50   $155.50  
  Purchase #7 $126.70   5.499%   $133.6672   $133.67   $133.65   $133.70  
  7 purchase totals = $943.34       $1,021.8992   $1,021.89   $1,021.90   $1,021.90