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 $113.47   7.375%   $121.8384   $121.84   $121.85   $121.80  
  Purchase #2 $224.52   10.135%   $247.2751   $247.28   $247.30   $247.30  
  Purchase #3 $121.58   10.572%   $134.4334   $134.43   $134.45   $134.40  
  Purchase #4 $172.81   10.688%   $191.2799   $191.28   $191.30   $191.30  
  Purchase #5 $14.76   12.713%   $16.6364   $16.64   $16.65   $16.60  
  Purchase #6 $107.43   4.488%   $112.2515   $112.25   $112.25   $112.30  
  Purchase #7 $157.72   4.860%   $165.3852   $165.39   $165.40   $165.40  
  7 purchase totals = $912.29       $989.0999   $989.11   $989.20   $989.10