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 $243.87   13.334%   $276.3876   $276.39   $276.40   $276.40  
  Purchase #2 $150.78   3.432%   $155.9548   $155.95   $155.95   $156.00  
  Purchase #3 $238.80   6.763%   $254.95   $254.95   $254.95   $255.00  
  Purchase #4 $72.77   3.342%   $75.202   $75.20   $75.20   $75.20  
  Purchase #5 $206.34   6.740%   $220.2473   $220.25   $220.25   $220.20  
  Purchase #6 $212.73   13.344%   $241.1167   $241.12   $241.10   $241.10  
  Purchase #7 $11.35   5.365%   $11.9589   $11.96   $11.95   $12.00  
  7 purchase totals = $1,136.64       $1,235.8173   $1,235.82   $1,235.80   $1,235.90