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 $43.67   6.590%   $46.5479   $46.55   $46.55   $46.50  
  Purchase #2 $228.80   4.762%   $239.6955   $239.70   $239.70   $239.70  
  Purchase #3 $145.47   13.849%   $165.6161   $165.62   $165.60   $165.60  
  Purchase #4 $140.72   4.732%   $147.3789   $147.38   $147.40   $147.40  
  Purchase #5 $194.59   5.846%   $205.9657   $205.97   $205.95   $206.00  
  Purchase #6 $8.90   5.342%   $9.3754   $9.38   $9.40   $9.40  
  Purchase #7 $18.84   9.236%   $20.5801   $20.58   $20.60   $20.60  
  7 purchase totals = $780.99       $835.1596   $835.18   $835.20   $835.20