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 $159.63   8.315%   $172.9032   $172.90   $172.90   $172.90  
  Purchase #2 $211.41   7.207%   $226.6463   $226.65   $226.65   $226.60  
  Purchase #3 $117.74   12.368%   $132.3021   $132.30   $132.30   $132.30  
  Purchase #4 $13.98   6.565%   $14.8978   $14.90   $14.90   $14.90  
  Purchase #5 $98.37   5.113%   $103.3997   $103.40   $103.40   $103.40  
  Purchase #6 $223.80   12.148%   $250.9872   $250.99   $251.00   $251.00  
  Purchase #7 $179.32   7.166%   $192.1701   $192.17   $192.15   $192.20  
  7 purchase totals = $1,004.25       $1,093.3064   $1,093.31   $1,093.30   $1,093.30