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 $243.75   13.221%   $275.9762   $275.98   $276.00   $276.00  
  Purchase #2 $159.76   3.753%   $165.7558   $165.76   $165.75   $165.80  
  Purchase #3 $17.85   12.408%   $20.0648   $20.06   $20.05   $20.10  
  Purchase #4 $210.30   7.553%   $226.184   $226.18   $226.20   $226.20  
  Purchase #5 $238.96   10.519%   $264.0962   $264.10   $264.10   $264.10  
  Purchase #6 $91.30   5.752%   $96.5516   $96.55   $96.55   $96.60  
  Purchase #7 $5.98   13.176%   $6.7679   $6.77   $6.75   $6.80  
  7 purchase totals = $967.90       $1,055.3965   $1,055.40   $1,055.40   $1,055.60