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 $59.32   11.203%   $65.9656   $65.97   $65.95   $66.00  
  Purchase #2 $73.79   11.777%   $82.4802   $82.48   $82.50   $82.50  
  Purchase #3 $181.78   11.149%   $202.0467   $202.05   $202.05   $202.00  
  Purchase #4 $71.98   3.549%   $74.5346   $74.53   $74.55   $74.50  
  Purchase #5 $229.41   5.271%   $241.5022   $241.50   $241.50   $241.50  
  Purchase #6 $154.46   13.226%   $174.8889   $174.89   $174.90   $174.90  
  Purchase #7 $243.91   12.627%   $274.7085   $274.71   $274.70   $274.70  
  7 purchase totals = $1,014.65       $1,116.1267   $1,116.13   $1,116.15   $1,116.10