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 $82.47   11.467%   $91.9268   $91.93   $91.95   $91.90  
  Purchase #2 $161.72   7.374%   $173.6452   $173.65   $173.65   $173.60  
  Purchase #3 $88.73   11.414%   $98.8576   $98.86   $98.85   $98.90  
  Purchase #4 $145.47   4.398%   $151.8678   $151.87   $151.85   $151.90  
  Purchase #5 $10.41   6.475%   $11.084   $11.08   $11.10   $11.10  
  Purchase #6 $205.48   12.486%   $231.1362   $231.14   $231.15   $231.10  
  Purchase #7 $195.77   3.620%   $202.8569   $202.86   $202.85   $202.90  
  7 purchase totals = $890.05       $961.3745   $961.39   $961.40   $961.40