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 $187.46   5.196%   $197.2004   $197.20   $197.20   $197.20  
  Purchase #2 $203.55   3.581%   $210.8391   $210.84   $210.85   $210.80  
  Purchase #3 $124.60   5.849%   $131.8879   $131.89   $131.90   $131.90  
  Purchase #4 $208.74   4.474%   $218.079   $218.08   $218.10   $218.10  
  Purchase #5 $82.88   7.153%   $88.8084   $88.81   $88.80   $88.80  
  Purchase #6 $186.97   3.610%   $193.7196   $193.72   $193.70   $193.70  
  Purchase #7 $218.94   9.618%   $239.9976   $240.00   $240.00   $240.00  
  7 purchase totals = $1,213.14       $1,280.5320   $1,280.54   $1,280.55   $1,280.50