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 $196.85   10.702%   $217.9169   $217.92   $217.90   $217.90  
  Purchase #2 $220.83   6.343%   $234.8372   $234.84   $234.85   $234.80  
  Purchase #3 $83.43   10.373%   $92.0842   $92.08   $92.10   $92.10  
  Purchase #4 $246.59   12.673%   $277.8404   $277.84   $277.85   $277.80  
  Purchase #5 $103.58   8.757%   $112.6505   $112.65   $112.65   $112.70  
  Purchase #6 $177.95   9.316%   $194.5278   $194.53   $194.55   $194.50  
  Purchase #7 $198.79   4.266%   $207.2704   $207.27   $207.25   $207.30  
  7 purchase totals = $1,228.02       $1,337.1274   $1,337.13   $1,337.15   $1,337.10