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 $90.52   3.866%   $94.0195   $94.02   $94.00   $94.00  
  Purchase #2 $208.83   5.615%   $220.5558   $220.56   $220.55   $220.60  
  Purchase #3 $145.86   13.563%   $165.643   $165.64   $165.65   $165.60  
  Purchase #4 $169.95   13.550%   $192.9782   $192.98   $193.00   $193.00  
  Purchase #5 $230.96   10.405%   $254.9914   $254.99   $255.00   $255.00  
  Purchase #6 $37.54   13.660%   $42.668   $42.67   $42.65   $42.70  
  Purchase #7 $159.42   11.874%   $178.3495   $178.35   $178.35   $178.30  
  7 purchase totals = $1,043.08       $1,149.2054   $1,149.21   $1,149.20   $1,149.20