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 $61.74   7.256%   $66.2199   $66.22   $66.20   $66.20  
  Purchase #2 $126.84   4.679%   $132.7748   $132.77   $132.75   $132.80  
  Purchase #3 $81.42   12.179%   $91.3361   $91.34   $91.35   $91.30  
  Purchase #4 $123.84   9.175%   $135.2023   $135.20   $135.20   $135.20  
  Purchase #5 $161.84   11.845%   $181.0099   $181.01   $181.00   $181.00  
  Purchase #6 $57.81   12.422%   $64.9912   $64.99   $65.00   $65.00  
  Purchase #7 $155.65   10.416%   $171.8625   $171.86   $171.85   $171.90  
  7 purchase totals = $769.14       $843.3967   $843.39   $843.35   $843.40