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 $247.98   7.785%   $267.2852   $267.29   $267.30   $267.30  
  Purchase #2 $63.92   7.276%   $68.5708   $68.57   $68.55   $68.60  
  Purchase #3 $94.68   3.165%   $97.6766   $97.68   $97.70   $97.70  
  Purchase #4 $234.92   9.672%   $257.6415   $257.64   $257.65   $257.60  
  Purchase #5 $115.67   7.217%   $124.0179   $124.02   $124.00   $124.00  
  Purchase #6 $193.59   4.356%   $202.0228   $202.02   $202.00   $202.00  
  Purchase #7 $199.87   10.413%   $220.6825   $220.68   $220.70   $220.70  
  7 purchase totals = $1,150.63       $1,237.8973   $1,237.90   $1,237.90   $1,237.90