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 $197.52   6.323%   $210.0092   $210.01   $210.00   $210.00  
  Purchase #2 $195.75   6.161%   $207.8102   $207.81   $207.80   $207.80  
  Purchase #3 $174.90   7.267%   $187.61   $187.61   $187.60   $187.60  
  Purchase #4 $135.29   4.748%   $141.7136   $141.71   $141.70   $141.70  
  Purchase #5 $50.27   11.246%   $55.9234   $55.92   $55.90   $55.90  
  Purchase #6 $206.40   10.641%   $228.363   $228.36   $228.35   $228.40  
  Purchase #7 $15.33   9.106%   $16.7259   $16.73   $16.75   $16.70  
  7 purchase totals = $975.46       $1,048.1553   $1,048.15   $1,048.10   $1,048.10