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 $81.61   13.668%   $92.7645   $92.76   $92.75   $92.80  
  Purchase #2 $223.32   5.578%   $235.7768   $235.78   $235.80   $235.80  
  Purchase #3 $219.70   11.312%   $244.5525   $244.55   $244.55   $244.60  
  Purchase #4 $161.27   6.794%   $172.2267   $172.23   $172.25   $172.20  
  Purchase #5 $210.64   7.859%   $227.1942   $227.19   $227.20   $227.20  
  Purchase #6 $63.69   3.600%   $65.9828   $65.98   $66.00   $66.00  
  Purchase #7 $220.39   4.523%   $230.3582   $230.36   $230.35   $230.40  
  7 purchase totals = $1,180.62       $1,268.8557   $1,268.85   $1,268.90   $1,269.00