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 $93.63   13.270%   $106.0547   $106.05   $106.05   $106.10  
  Purchase #2 $219.53   10.858%   $243.3666   $243.37   $243.35   $243.40  
  Purchase #3 $132.57   3.381%   $137.0522   $137.05   $137.05   $137.10  
  Purchase #4 $150.60   4.479%   $157.3454   $157.35   $157.35   $157.30  
  Purchase #5 $123.77   7.283%   $132.7842   $132.78   $132.80   $132.80  
  Purchase #6 $193.47   6.450%   $205.9488   $205.95   $205.95   $205.90  
  Purchase #7 $65.71   13.250%   $74.4166   $74.42   $74.40   $74.40  
  7 purchase totals = $979.28       $1,056.9685   $1,056.97   $1,056.95   $1,057.00