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 $198.77   6.169%   $211.0321   $211.03   $211.05   $211.00  
  Purchase #2 $66.44   9.839%   $72.977   $72.98   $73.00   $73.00  
  Purchase #3 $126.72   7.196%   $135.8388   $135.84   $135.85   $135.80  
  Purchase #4 $56.65   7.480%   $60.8874   $60.89   $60.90   $60.90  
  Purchase #5 $75.67   13.559%   $85.9301   $85.93   $85.95   $85.90  
  Purchase #6 $105.28   10.599%   $116.4386   $116.44   $116.45   $116.40  
  Purchase #7 $66.49   6.457%   $70.7833   $70.78   $70.80   $70.80  
  7 purchase totals = $696.02       $753.8873   $753.89   $754.00   $753.80