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 $142.64   12.343%   $160.2461   $160.25   $160.25   $160.20  
  Purchase #2 $210.65   7.642%   $226.7479   $226.75   $226.75   $226.70  
  Purchase #3 $155.56   11.305%   $173.1461   $173.15   $173.15   $173.10  
  Purchase #4 $94.30   7.850%   $101.7026   $101.70   $101.70   $101.70  
  Purchase #5 $14.37   9.460%   $15.7294   $15.73   $15.75   $15.70  
  Purchase #6 $155.81   13.866%   $177.4146   $177.41   $177.40   $177.40  
  Purchase #7 $152.90   6.299%   $162.5312   $162.53   $162.55   $162.50  
  7 purchase totals = $926.23       $1,017.5179   $1,017.52   $1,017.55   $1,017.30