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 $98.62   5.210%   $103.7581   $103.76   $103.75   $103.80  
  Purchase #2 $179.35   6.282%   $190.6168   $190.62   $190.60   $190.60  
  Purchase #3 $157.62   6.135%   $167.29   $167.29   $167.30   $167.30  
  Purchase #4 $132.31   7.582%   $142.3417   $142.34   $142.35   $142.30  
  Purchase #5 $27.53   10.752%   $30.49   $30.49   $30.50   $30.50  
  Purchase #6 $23.30   7.237%   $24.9862   $24.99   $25.00   $25.00  
  Purchase #7 $11.71   3.122%   $12.0756   $12.08   $12.10   $12.10  
  7 purchase totals = $630.44       $671.5584   $671.57   $671.60   $671.60