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 $92.58   4.294%   $96.5554   $96.56   $96.55   $96.60  
  Purchase #2 $146.83   10.667%   $162.4924   $162.49   $162.50   $162.50  
  Purchase #3 $90.61   5.155%   $95.2809   $95.28   $95.30   $95.30  
  Purchase #4 $144.84   3.190%   $149.4604   $149.46   $149.45   $149.50  
  Purchase #5 $68.79   5.740%   $72.7385   $72.74   $72.75   $72.70  
  Purchase #6 $56.31   6.865%   $60.1757   $60.18   $60.20   $60.20  
  Purchase #7 $203.80   10.517%   $225.2336   $225.23   $225.25   $225.20  
  7 purchase totals = $803.76       $861.9369   $861.94   $862.00   $862.00