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 $210.39   11.127%   $233.8001   $233.80   $233.80   $233.80  
  Purchase #2 $145.81   10.557%   $161.2032   $161.20   $161.20   $161.20  
  Purchase #3 $130.56   3.275%   $134.8358   $134.84   $134.85   $134.80  
  Purchase #4 $185.48   5.548%   $195.7704   $195.77   $195.75   $195.80  
  Purchase #5 $243.86   3.176%   $251.605   $251.61   $251.60   $251.60  
  Purchase #6 $138.78   8.439%   $150.4916   $150.49   $150.50   $150.50  
  Purchase #7 $87.55   8.600%   $95.0793   $95.08   $95.10   $95.10  
  7 purchase totals = $1,142.43       $1,222.7854   $1,222.79   $1,222.80   $1,222.80