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 $84.78   10.528%   $93.7056   $93.71   $93.70   $93.70  
  Purchase #2 $243.63   5.618%   $257.3171   $257.32   $257.30   $257.30  
  Purchase #3 $193.62   10.775%   $214.4826   $214.48   $214.50   $214.50  
  Purchase #4 $56.92   3.615%   $58.9777   $58.98   $59.00   $59.00  
  Purchase #5 $189.92   8.170%   $205.4365   $205.44   $205.45   $205.40  
  Purchase #6 $234.44   10.209%   $258.374   $258.37   $258.35   $258.40  
  Purchase #7 $181.52   5.723%   $191.9084   $191.91   $191.90   $191.90  
  7 purchase totals = $1,184.83       $1,280.2019   $1,280.21   $1,280.20   $1,280.20