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 $118.67   7.633%   $127.7281   $127.73   $127.75   $127.70  
  Purchase #2 $93.86   8.626%   $101.9564   $101.96   $101.95   $102.00  
  Purchase #3 $64.61   6.810%   $69.0099   $69.01   $69.00   $69.00  
  Purchase #4 $242.59   5.731%   $256.4928   $256.49   $256.50   $256.50  
  Purchase #5 $13.57   5.631%   $14.3341   $14.33   $14.35   $14.30  
  Purchase #6 $199.62   5.771%   $211.1401   $211.14   $211.15   $211.10  
  Purchase #7 $225.70   9.320%   $246.7352   $246.74   $246.75   $246.70  
  7 purchase totals = $958.62       $1,027.3966   $1,027.40   $1,027.45   $1,027.30