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 $172.31   13.627%   $195.7907   $195.79   $195.80   $195.80  
  Purchase #2 $89.44   9.700%   $98.1157   $98.12   $98.10   $98.10  
  Purchase #3 $13.28   8.279%   $14.3795   $14.38   $14.40   $14.40  
  Purchase #4 $41.74   4.660%   $43.6851   $43.69   $43.70   $43.70  
  Purchase #5 $209.27   6.774%   $223.4459   $223.45   $223.45   $223.40  
  Purchase #6 $183.62   10.703%   $203.2728   $203.27   $203.25   $203.30  
  Purchase #7 $211.51   12.359%   $237.6505   $237.65   $237.65   $237.70  
  7 purchase totals = $921.17       $1,016.3402   $1,016.35   $1,016.35   $1,016.40