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 $228.44   11.247%   $254.1326   $254.13   $254.15   $254.10  
  Purchase #2 $211.45   6.566%   $225.3338   $225.33   $225.35   $225.30  
  Purchase #3 $232.37   4.446%   $242.7012   $242.70   $242.70   $242.70  
  Purchase #4 $237.82   3.717%   $246.6598   $246.66   $246.65   $246.70  
  Purchase #5 $128.62   10.353%   $141.936   $141.94   $141.95   $141.90  
  Purchase #6 $65.94   12.800%   $74.3803   $74.38   $74.40   $74.40  
  Purchase #7 $97.82   12.130%   $109.6856   $109.69   $109.70   $109.70  
  7 purchase totals = $1,202.46       $1,294.8293   $1,294.83   $1,294.90   $1,294.80