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 $87.44   11.700%   $97.6705   $97.67   $97.65   $97.70  
  Purchase #2 $129.49   9.491%   $141.7799   $141.78   $141.80   $141.80  
  Purchase #3 $109.55   12.852%   $123.6294   $123.63   $123.65   $123.60  
  Purchase #4 $70.40   7.480%   $75.6659   $75.67   $75.65   $75.70  
  Purchase #5 $33.77   8.762%   $36.7289   $36.73   $36.75   $36.70  
  Purchase #6 $205.92   6.299%   $218.8909   $218.89   $218.90   $218.90  
  Purchase #7 $165.27   9.269%   $180.5889   $180.59   $180.60   $180.60  
  7 purchase totals = $801.84       $874.9544   $874.96   $875.00   $875.00