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 $82.84   13.564%   $94.0764   $94.08   $94.10   $94.10  
  Purchase #2 $24.29   8.291%   $26.3039   $26.30   $26.30   $26.30  
  Purchase #3 $212.34   12.168%   $238.1775   $238.18   $238.20   $238.20  
  Purchase #4 $247.94   6.424%   $263.8677   $263.87   $263.85   $263.90  
  Purchase #5 $56.91   11.568%   $63.4933   $63.49   $63.50   $63.50  
  Purchase #6 $181.42   12.205%   $203.5623   $203.56   $203.55   $203.60  
  Purchase #7 $78.85   7.275%   $84.5863   $84.59   $84.60   $84.60  
  7 purchase totals = $884.59       $974.0674   $974.07   $974.10   $974.20