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 $52.27   12.259%   $58.6778   $58.68   $58.70   $58.70  
  Purchase #2 $203.78   7.151%   $218.3523   $218.35   $218.35   $218.40  
  Purchase #3 $149.28   4.662%   $156.2394   $156.24   $156.25   $156.20  
  Purchase #4 $108.52   9.143%   $118.442   $118.44   $118.45   $118.40  
  Purchase #5 $68.28   5.398%   $71.9658   $71.97   $71.95   $72.00  
  Purchase #6 $135.75   13.642%   $154.269   $154.27   $154.25   $154.30  
  Purchase #7 $60.40   7.153%   $64.7204   $64.72   $64.70   $64.70  
  7 purchase totals = $778.28       $842.6667   $842.67   $842.65   $842.70