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 $162.99   13.301%   $184.6693   $184.67   $184.65   $184.70  
  Purchase #2 $144.44   4.245%   $150.5715   $150.57   $150.55   $150.60  
  Purchase #3 $72.31   7.643%   $77.8367   $77.84   $77.85   $77.80  
  Purchase #4 $201.95   8.769%   $219.659   $219.66   $219.65   $219.70  
  Purchase #5 $12.85   10.784%   $14.2357   $14.24   $14.25   $14.20  
  Purchase #6 $213.67   12.607%   $240.6074   $240.61   $240.60   $240.60  
  Purchase #7 $154.26   13.701%   $175.3952   $175.40   $175.40   $175.40  
  7 purchase totals = $962.47       $1,062.9748   $1,062.99   $1,062.95   $1,063.00