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 $60.29   7.575%   $64.857   $64.86   $64.85   $64.90  
  Purchase #2 $167.42   4.724%   $175.3289   $175.33   $175.35   $175.30  
  Purchase #3 $6.62   7.391%   $7.1093   $7.11   $7.10   $7.10  
  Purchase #4 $224.27   8.538%   $243.4182   $243.42   $243.40   $243.40  
  Purchase #5 $97.73   8.475%   $106.0126   $106.01   $106.00   $106.00  
  Purchase #6 $86.85   7.390%   $93.2682   $93.27   $93.25   $93.30  
  Purchase #7 $159.31   13.805%   $181.3027   $181.30   $181.30   $181.30  
  7 purchase totals = $802.49       $871.2969   $871.30   $871.25   $871.30