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 $84.43   9.449%   $92.4078   $92.41   $92.40   $92.40  
  Purchase #2 $110.95   13.195%   $125.5899   $125.59   $125.60   $125.60  
  Purchase #3 $240.54   11.219%   $267.5262   $267.53   $267.55   $267.50  
  Purchase #4 $122.82   4.181%   $127.9551   $127.96   $127.95   $128.00  
  Purchase #5 $103.55   4.207%   $107.9063   $107.91   $107.90   $107.90  
  Purchase #6 $180.81   12.302%   $203.0532   $203.05   $203.05   $203.10  
  Purchase #7 $218.82   6.475%   $232.9886   $232.99   $233.00   $233.00  
  7 purchase totals = $1,061.92       $1,157.4271   $1,157.44   $1,157.45   $1,157.50