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 $30.41   9.528%   $33.3075   $33.31   $33.30   $33.30  
  Purchase #2 $177.47   13.707%   $201.7958   $201.80   $201.80   $201.80  
  Purchase #3 $208.27   9.743%   $228.5617   $228.56   $228.55   $228.60  
  Purchase #4 $22.67   8.124%   $24.5117   $24.51   $24.50   $24.50  
  Purchase #5 $170.41   11.244%   $189.5709   $189.57   $189.55   $189.60  
  Purchase #6 $230.65   6.434%   $245.49   $245.49   $245.50   $245.50  
  Purchase #7 $94.48   5.229%   $99.4204   $99.42   $99.40   $99.40  
  7 purchase totals = $934.36       $1,022.6580   $1,022.66   $1,022.60   $1,022.70