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 $223.33   11.776%   $249.6293   $249.63   $249.65   $249.60  
  Purchase #2 $250.52   10.452%   $276.7044   $276.70   $276.70   $276.70  
  Purchase #3 $124.46   10.865%   $137.9826   $137.98   $138.00   $138.00  
  Purchase #4 $107.95   5.386%   $113.7642   $113.76   $113.75   $113.80  
  Purchase #5 $80.74   12.851%   $91.1159   $91.12   $91.10   $91.10  
  Purchase #6 $42.46   5.204%   $44.6696   $44.67   $44.65   $44.70  
  Purchase #7 $217.78   11.425%   $242.6614   $242.66   $242.65   $242.70  
  7 purchase totals = $1,047.24       $1,156.5274   $1,156.52   $1,156.50   $1,156.60