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 $184.76   13.825%   $210.3031   $210.30   $210.30   $210.30  
  Purchase #2 $153.32   9.332%   $167.6278   $167.63   $167.65   $167.60  
  Purchase #3 $197.87   8.545%   $214.778   $214.78   $214.80   $214.80  
  Purchase #4 $233.48   4.766%   $244.6077   $244.61   $244.60   $244.60  
  Purchase #5 $53.43   5.390%   $56.3099   $56.31   $56.30   $56.30  
  Purchase #6 $10.43   5.751%   $11.0298   $11.03   $11.05   $11.00  
  Purchase #7 $144.84   10.816%   $160.5059   $160.51   $160.50   $160.50  
  7 purchase totals = $978.13       $1,065.1622   $1,065.17   $1,065.20   $1,065.10