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 $227.52   11.785%   $254.3332   $254.33   $254.35   $254.30  
  Purchase #2 $24.34   8.742%   $26.4678   $26.47   $26.45   $26.50  
  Purchase #3 $37.91   13.532%   $43.04   $43.04   $43.05   $43.00  
  Purchase #4 $171.27   3.730%   $177.6584   $177.66   $177.65   $177.70  
  Purchase #5 $150.96   10.239%   $166.4168   $166.42   $166.40   $166.40  
  Purchase #6 $72.62   8.695%   $78.9343   $78.93   $78.95   $78.90  
  Purchase #7 $247.97   12.118%   $278.019   $278.02   $278.00   $278.00  
  7 purchase totals = $932.59       $1,024.8695   $1,024.87   $1,024.85   $1,024.80