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 $206.35   6.107%   $218.9518   $218.95   $218.95   $219.00  
  Purchase #2 $170.48   3.742%   $176.8594   $176.86   $176.85   $176.90  
  Purchase #3 $57.26   12.541%   $64.441   $64.44   $64.45   $64.40  
  Purchase #4 $69.25   4.164%   $72.1336   $72.13   $72.15   $72.10  
  Purchase #5 $150.29   7.499%   $161.5602   $161.56   $161.55   $161.60  
  Purchase #6 $194.64   10.374%   $214.832   $214.83   $214.85   $214.80  
  Purchase #7 $200.34   5.692%   $211.7434   $211.74   $211.75   $211.70  
  7 purchase totals = $1,048.61       $1,120.5214   $1,120.51   $1,120.55   $1,120.50