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 $213.33   6.335%   $226.8445   $226.84   $226.85   $226.80  
  Purchase #2 $60.65   6.596%   $64.6505   $64.65   $64.65   $64.70  
  Purchase #3 $102.26   4.245%   $106.6009   $106.60   $106.60   $106.60  
  Purchase #4 $172.30   4.820%   $180.6049   $180.60   $180.60   $180.60  
  Purchase #5 $229.64   10.386%   $253.4904   $253.49   $253.50   $253.50  
  Purchase #6 $130.65   7.487%   $140.4318   $140.43   $140.45   $140.40  
  Purchase #7 $67.63   12.773%   $76.2684   $76.27   $76.25   $76.30  
  7 purchase totals = $976.46       $1,048.8914   $1,048.88   $1,048.90   $1,048.90