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 $154.34   13.642%   $175.3951   $175.40   $175.40   $175.40  
  Purchase #2 $60.35   13.675%   $68.6029   $68.60   $68.60   $68.60  
  Purchase #3 $235.64   10.492%   $260.3633   $260.36   $260.35   $260.40  
  Purchase #4 $88.70   6.862%   $94.7866   $94.79   $94.80   $94.80  
  Purchase #5 $23.65   10.349%   $26.0975   $26.10   $26.10   $26.10  
  Purchase #6 $165.36   6.603%   $176.2787   $176.28   $176.30   $176.30  
  Purchase #7 $23.82   5.235%   $25.067   $25.07   $25.05   $25.10  
  7 purchase totals = $751.86       $826.5911   $826.60   $826.60   $826.70