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 $60.32   9.117%   $65.8194   $65.82   $65.80   $65.80  
  Purchase #2 $172.31   13.169%   $195.0015   $195.00   $195.00   $195.00  
  Purchase #3 $218.37   7.406%   $234.5425   $234.54   $234.55   $234.50  
  Purchase #4 $212.50   4.874%   $222.8573   $222.86   $222.85   $222.90  
  Purchase #5 $223.68   8.770%   $243.2967   $243.30   $243.30   $243.30  
  Purchase #6 $167.91   9.648%   $184.11   $184.11   $184.10   $184.10  
  Purchase #7 $10.97   5.605%   $11.5849   $11.58   $11.60   $11.60  
  7 purchase totals = $1,066.06       $1,157.2123   $1,157.21   $1,157.20   $1,157.20