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 $93.95   8.147%   $101.6041   $101.60   $101.60   $101.60  
  Purchase #2 $66.54   7.779%   $71.7161   $71.72   $71.70   $71.70  
  Purchase #3 $181.43   7.513%   $195.0608   $195.06   $195.05   $195.10  
  Purchase #4 $137.31   7.692%   $147.8719   $147.87   $147.85   $147.90  
  Purchase #5 $248.44   7.432%   $266.9041   $266.90   $266.90   $266.90  
  Purchase #6 $121.33   10.419%   $133.9714   $133.97   $133.95   $134.00  
  Purchase #7 $105.73   12.309%   $118.7443   $118.74   $118.75   $118.70  
  7 purchase totals = $954.73       $1,035.8727   $1,035.86   $1,035.80   $1,035.90