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 $245.68   13.553%   $278.977   $278.98   $279.00   $279.00  
  Purchase #2 $66.36   8.336%   $71.8918   $71.89   $71.90   $71.90  
  Purchase #3 $43.35   13.745%   $49.3085   $49.31   $49.30   $49.30  
  Purchase #4 $210.69   10.819%   $233.4846   $233.48   $233.50   $233.50  
  Purchase #5 $110.85   7.464%   $119.1238   $119.12   $119.10   $119.10  
  Purchase #6 $154.51   12.511%   $173.8407   $173.84   $173.85   $173.80  
  Purchase #7 $117.33   12.708%   $132.2403   $132.24   $132.25   $132.20  
  7 purchase totals = $948.77       $1,058.8667   $1,058.86   $1,058.90   $1,058.80