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 $54.71   13.550%   $62.1232   $62.12   $62.10   $62.10  
  Purchase #2 $220.36   3.817%   $228.7711   $228.77   $228.75   $228.80  
  Purchase #3 $188.97   6.564%   $201.374   $201.37   $201.35   $201.40  
  Purchase #4 $73.32   10.712%   $81.174   $81.17   $81.15   $81.20  
  Purchase #5 $145.52   7.454%   $156.3671   $156.37   $156.35   $156.40  
  Purchase #6 $17.45   6.426%   $18.5713   $18.57   $18.55   $18.60  
  Purchase #7 $19.44   6.288%   $20.6624   $20.66   $20.65   $20.70  
  7 purchase totals = $719.77       $769.0431   $769.03   $768.90   $769.20