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 $87.69   12.433%   $98.5925   $98.59   $98.60   $98.60  
  Purchase #2 $142.46   8.447%   $154.4936   $154.49   $154.50   $154.50  
  Purchase #3 $198.82   12.519%   $223.7103   $223.71   $223.70   $223.70  
  Purchase #4 $158.49   9.852%   $174.1044   $174.10   $174.10   $174.10  
  Purchase #5 $156.59   6.766%   $167.1849   $167.18   $167.20   $167.20  
  Purchase #6 $144.31   3.415%   $149.2382   $149.24   $149.25   $149.20  
  Purchase #7 $111.33   12.514%   $125.2618   $125.26   $125.25   $125.30  
  7 purchase totals = $999.69       $1,092.5857   $1,092.57   $1,092.60   $1,092.60