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 $53.98   5.327%   $56.8555   $56.86   $56.85   $56.90  
  Purchase #2 $235.72   3.193%   $243.2465   $243.25   $243.25   $243.20  
  Purchase #3 $192.88   10.207%   $212.5673   $212.57   $212.55   $212.60  
  Purchase #4 $74.74   8.239%   $80.8978   $80.90   $80.90   $80.90  
  Purchase #5 $118.73   4.496%   $124.0681   $124.07   $124.05   $124.10  
  Purchase #6 $130.72   3.382%   $135.141   $135.14   $135.15   $135.10  
  Purchase #7 $236.38   3.567%   $244.8117   $244.81   $244.80   $244.80  
  7 purchase totals = $1,043.15       $1,097.5879   $1,097.60   $1,097.55   $1,097.60