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 $147.69   13.245%   $167.2515   $167.25   $167.25   $167.30  
  Purchase #2 $63.94   3.268%   $66.0296   $66.03   $66.05   $66.00  
  Purchase #3 $46.44   13.788%   $52.8431   $52.84   $52.85   $52.80  
  Purchase #4 $247.64   4.851%   $259.653   $259.65   $259.65   $259.70  
  Purchase #5 $239.66   10.563%   $264.9753   $264.98   $265.00   $265.00  
  Purchase #6 $11.54   9.146%   $12.5954   $12.60   $12.60   $12.60  
  Purchase #7 $194.70   9.180%   $212.5735   $212.57   $212.55   $212.60  
  7 purchase totals = $951.61       $1,035.9214   $1,035.92   $1,035.95   $1,036.00