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 $188.70   12.794%   $212.8423   $212.84   $212.85   $212.80  
  Purchase #2 $224.92   7.292%   $241.3212   $241.32   $241.30   $241.30  
  Purchase #3 $195.29   6.297%   $207.5874   $207.59   $207.60   $207.60  
  Purchase #4 $23.90   9.107%   $26.0766   $26.08   $26.10   $26.10  
  Purchase #5 $85.87   13.385%   $97.3637   $97.36   $97.35   $97.40  
  Purchase #6 $43.78   6.115%   $46.4571   $46.46   $46.45   $46.50  
  Purchase #7 $201.47   5.133%   $211.8115   $211.81   $211.80   $211.80  
  7 purchase totals = $963.93       $1,043.4598   $1,043.46   $1,043.45   $1,043.50