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 $61.59   11.356%   $68.5842   $68.58   $68.60   $68.60  
  Purchase #2 $52.32   10.337%   $57.7283   $57.73   $57.75   $57.70  
  Purchase #3 $84.30   4.795%   $88.3422   $88.34   $88.35   $88.30  
  Purchase #4 $36.70   4.180%   $38.2341   $38.23   $38.25   $38.20  
  Purchase #5 $60.96   11.567%   $68.0112   $68.01   $68.00   $68.00  
  Purchase #6 $82.34   8.303%   $89.1767   $89.18   $89.20   $89.20  
  Purchase #7 $46.58   9.363%   $50.9413   $50.94   $50.95   $50.90  
  7 purchase totals = $424.79       $461.0180   $461.01   $461.10   $460.90