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 $83.59   10.791%   $92.6102   $92.61   $92.60   $92.60  
  Purchase #2 $219.80   11.269%   $244.5693   $244.57   $244.55   $244.60  
  Purchase #3 $10.46   9.329%   $11.4358   $11.44   $11.45   $11.40  
  Purchase #4 $152.61   4.677%   $159.7476   $159.75   $159.75   $159.70  
  Purchase #5 $181.51   13.470%   $205.9594   $205.96   $205.95   $206.00  
  Purchase #6 $157.65   7.453%   $169.3997   $169.40   $169.40   $169.40  
  Purchase #7 $176.29   13.571%   $200.2143   $200.21   $200.20   $200.20  
  7 purchase totals = $981.91       $1,083.9363   $1,083.94   $1,083.90   $1,083.90