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 $59.38   11.737%   $66.3494   $66.35   $66.35   $66.30  
  Purchase #2 $244.59   12.422%   $274.973   $274.97   $274.95   $275.00  
  Purchase #3 $201.82   4.828%   $211.5639   $211.56   $211.55   $211.60  
  Purchase #4 $200.51   3.569%   $207.6662   $207.67   $207.65   $207.70  
  Purchase #5 $151.69   8.823%   $165.0736   $165.07   $165.05   $165.10  
  Purchase #6 $105.39   12.741%   $118.8177   $118.82   $118.80   $118.80  
  Purchase #7 $239.70   6.361%   $254.9473   $254.95   $254.95   $254.90  
  7 purchase totals = $1,203.08       $1,299.3911   $1,299.39   $1,299.30   $1,299.40