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 $235.54   13.667%   $267.7313   $267.73   $267.75   $267.70  
  Purchase #2 $119.66   7.231%   $128.3126   $128.31   $128.30   $128.30  
  Purchase #3 $98.42   5.115%   $103.4542   $103.45   $103.45   $103.50  
  Purchase #4 $162.25   13.412%   $184.011   $184.01   $184.00   $184.00  
  Purchase #5 $245.85   12.380%   $276.2862   $276.29   $276.30   $276.30  
  Purchase #6 $47.70   12.288%   $53.5614   $53.56   $53.55   $53.60  
  Purchase #7 $169.97   6.377%   $180.809   $180.81   $180.80   $180.80  
  7 purchase totals = $1,079.39       $1,194.1657   $1,194.16   $1,194.15   $1,194.20