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 $85.41   13.658%   $97.0753   $97.08   $97.10   $97.10  
  Purchase #2 $91.70   8.398%   $99.401   $99.40   $99.40   $99.40  
  Purchase #3 $58.32   3.502%   $60.3624   $60.36   $60.35   $60.40  
  Purchase #4 $147.32   10.615%   $162.958   $162.96   $162.95   $163.00  
  Purchase #5 $194.42   10.407%   $214.6533   $214.65   $214.65   $214.70  
  Purchase #6 $160.37   6.504%   $170.8005   $170.80   $170.80   $170.80  
  Purchase #7 $129.72   6.174%   $137.7289   $137.73   $137.75   $137.70  
  7 purchase totals = $867.26       $942.9794   $942.98   $943.00   $943.10