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 $106.42   11.623%   $118.7892   $118.79   $118.80   $118.80  
  Purchase #2 $207.26   13.222%   $234.6639   $234.66   $234.65   $234.70  
  Purchase #3 $109.74   12.395%   $123.3423   $123.34   $123.35   $123.30  
  Purchase #4 $51.95   10.163%   $57.2297   $57.23   $57.25   $57.20  
  Purchase #5 $196.84   5.347%   $207.365   $207.37   $207.35   $207.40  
  Purchase #6 $18.68   11.651%   $20.8564   $20.86   $20.85   $20.90  
  Purchase #7 $94.79   13.503%   $107.5895   $107.59   $107.60   $107.60  
  7 purchase totals = $785.68       $869.8360   $869.84   $869.85   $869.90