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 $248.34   6.626%   $264.795   $264.80   $264.80   $264.80  
  Purchase #2 $6.29   6.585%   $6.7042   $6.70   $6.70   $6.70  
  Purchase #3 $67.90   10.586%   $75.0879   $75.09   $75.10   $75.10  
  Purchase #4 $174.51   9.360%   $190.8441   $190.84   $190.85   $190.80  
  Purchase #5 $84.85   6.334%   $90.2244   $90.22   $90.20   $90.20  
  Purchase #6 $216.55   11.159%   $240.7148   $240.71   $240.70   $240.70  
  Purchase #7 $176.52   4.387%   $184.2639   $184.26   $184.25   $184.30  
  7 purchase totals = $974.96       $1,052.6343   $1,052.62   $1,052.60   $1,052.60