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 $206.59   8.344%   $223.8279   $223.83   $223.85   $223.80  
  Purchase #2 $197.31   3.759%   $204.7269   $204.73   $204.75   $204.70  
  Purchase #3 $22.49   10.175%   $24.7784   $24.78   $24.80   $24.80  
  Purchase #4 $242.63   9.301%   $265.197   $265.20   $265.20   $265.20  
  Purchase #5 $205.97   8.175%   $222.808   $222.81   $222.80   $222.80  
  Purchase #6 $24.53   6.127%   $26.033   $26.03   $26.05   $26.00  
  Purchase #7 $231.59   5.214%   $243.6651   $243.67   $243.65   $243.70  
  7 purchase totals = $1,131.11       $1,211.0363   $1,211.05   $1,211.10   $1,211.00