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 $168.97   10.654%   $186.9721   $186.97   $186.95   $187.00  
  Purchase #2 $83.36   5.761%   $88.1624   $88.16   $88.15   $88.20  
  Purchase #3 $166.43   10.207%   $183.4175   $183.42   $183.40   $183.40  
  Purchase #4 $202.93   13.103%   $229.5199   $229.52   $229.50   $229.50  
  Purchase #5 $153.62   11.432%   $171.1818   $171.18   $171.20   $171.20  
  Purchase #6 $213.46   13.366%   $241.9911   $241.99   $242.00   $242.00  
  Purchase #7 $60.98   5.204%   $64.1534   $64.15   $64.15   $64.20  
  7 purchase totals = $1,049.75       $1,165.3982   $1,165.39   $1,165.35   $1,165.50