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 $51.85   13.782%   $58.996   $59.00   $59.00   $59.00  
  Purchase #2 $172.29   12.442%   $193.7263   $193.73   $193.75   $193.70  
  Purchase #3 $43.97   13.388%   $49.8567   $49.86   $49.85   $49.90  
  Purchase #4 $234.69   7.714%   $252.794   $252.79   $252.80   $252.80  
  Purchase #5 $75.27   9.281%   $82.2558   $82.26   $82.25   $82.30  
  Purchase #6 $159.59   5.168%   $167.8376   $167.84   $167.85   $167.80  
  Purchase #7 $185.60   3.677%   $192.4245   $192.42   $192.40   $192.40  
  7 purchase totals = $923.26       $997.8909   $997.90   $997.90   $997.90