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 $186.47   8.861%   $202.9931   $202.99   $203.00   $203.00  
  Purchase #2 $31.58   10.141%   $34.7825   $34.78   $34.80   $34.80  
  Purchase #3 $182.93   3.302%   $188.9703   $188.97   $188.95   $189.00  
  Purchase #4 $249.52   7.345%   $267.8472   $267.85   $267.85   $267.80  
  Purchase #5 $73.60   10.214%   $81.1175   $81.12   $81.10   $81.10  
  Purchase #6 $104.46   7.122%   $111.8996   $111.90   $111.90   $111.90  
  Purchase #7 $120.27   4.692%   $125.9131   $125.91   $125.90   $125.90  
  7 purchase totals = $948.83       $1,013.5233   $1,013.52   $1,013.50   $1,013.50