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 $54.98   3.492%   $56.8999   $56.90   $56.90   $56.90  
  Purchase #2 $10.96   6.462%   $11.6682   $11.67   $11.65   $11.70  
  Purchase #3 $141.34   8.149%   $152.8578   $152.86   $152.85   $152.90  
  Purchase #4 $15.94   3.503%   $16.4984   $16.50   $16.50   $16.50  
  Purchase #5 $196.69   4.695%   $205.9246   $205.92   $205.90   $205.90  
  Purchase #6 $206.27   12.861%   $232.7984   $232.80   $232.80   $232.80  
  Purchase #7 $181.65   8.266%   $196.6652   $196.67   $196.65   $196.70  
  7 purchase totals = $807.83       $873.3125   $873.32   $873.25   $873.40