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 $216.57   13.283%   $245.337   $245.34   $245.35   $245.30  
  Purchase #2 $157.70   6.511%   $167.9678   $167.97   $167.95   $168.00  
  Purchase #3 $173.98   10.818%   $192.8012   $192.80   $192.80   $192.80  
  Purchase #4 $188.85   12.284%   $212.0483   $212.05   $212.05   $212.00  
  Purchase #5 $247.90   7.688%   $266.9586   $266.96   $266.95   $267.00  
  Purchase #6 $49.59   13.559%   $56.3139   $56.31   $56.30   $56.30  
  Purchase #7 $58.73   12.282%   $65.9432   $65.94   $65.95   $65.90  
  7 purchase totals = $1,093.32       $1,207.3700   $1,207.37   $1,207.35   $1,207.30