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 $81.96   13.470%   $93   $93.00   $93.00   $93.00  
  Purchase #2 $60.41   10.226%   $66.5875   $66.59   $66.60   $66.60  
  Purchase #3 $38.25   7.352%   $41.0621   $41.06   $41.05   $41.10  
  Purchase #4 $164.62   9.755%   $180.6787   $180.68   $180.70   $180.70  
  Purchase #5 $231.64   6.802%   $247.3962   $247.40   $247.40   $247.40  
  Purchase #6 $231.34   11.593%   $258.1592   $258.16   $258.15   $258.20  
  Purchase #7 $123.84   5.835%   $131.0661   $131.07   $131.05   $131.10  
  7 purchase totals = $932.06       $1,017.9498   $1,017.96   $1,017.95   $1,018.10