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 $215.61   8.313%   $233.5337   $233.53   $233.55   $233.50  
  Purchase #2 $191.68   6.769%   $204.6548   $204.65   $204.65   $204.70  
  Purchase #3 $90.33   8.442%   $97.9557   $97.96   $97.95   $98.00  
  Purchase #4 $173.86   5.550%   $183.5092   $183.51   $183.50   $183.50  
  Purchase #5 $87.39   13.502%   $99.1894   $99.19   $99.20   $99.20  
  Purchase #6 $181.26   3.652%   $187.8796   $187.88   $187.90   $187.90  
  Purchase #7 $10.62   8.715%   $11.5455   $11.55   $11.55   $11.50  
  7 purchase totals = $950.75       $1,018.2679   $1,018.27   $1,018.30   $1,018.30