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 $166.91   6.614%   $177.9494   $177.95   $177.95   $177.90  
  Purchase #2 $245.53   5.532%   $259.1127   $259.11   $259.10   $259.10  
  Purchase #3 $219.43   6.691%   $234.1121   $234.11   $234.10   $234.10  
  Purchase #4 $45.96   4.463%   $48.0112   $48.01   $48.00   $48.00  
  Purchase #5 $125.94   9.783%   $138.2607   $138.26   $138.25   $138.30  
  Purchase #6 $96.48   10.452%   $106.5641   $106.56   $106.55   $106.60  
  Purchase #7 $41.88   7.125%   $44.864   $44.86   $44.85   $44.90  
  7 purchase totals = $942.13       $1,008.8742   $1,008.86   $1,008.80   $1,008.90