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 $114.41   4.270%   $119.2953   $119.30   $119.30   $119.30  
  Purchase #2 $63.81   8.785%   $69.4157   $69.42   $69.40   $69.40  
  Purchase #3 $237.49   12.640%   $267.5087   $267.51   $267.50   $267.50  
  Purchase #4 $169.45   7.812%   $182.6874   $182.69   $182.70   $182.70  
  Purchase #5 $223.34   12.435%   $251.1123   $251.11   $251.10   $251.10  
  Purchase #6 $180.96   13.751%   $205.8438   $205.84   $205.85   $205.80  
  Purchase #7 $127.79   9.830%   $140.3518   $140.35   $140.35   $140.40  
  7 purchase totals = $1,117.25       $1,236.2150   $1,236.22   $1,236.20   $1,236.20