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 $250.62   10.192%   $276.1632   $276.16   $276.15   $276.20  
  Purchase #2 $187.55   9.388%   $205.1572   $205.16   $205.15   $205.20  
  Purchase #3 $155.26   11.241%   $172.7128   $172.71   $172.70   $172.70  
  Purchase #4 $120.60   9.208%   $131.7048   $131.70   $131.70   $131.70  
  Purchase #5 $56.82   11.213%   $63.1912   $63.19   $63.20   $63.20  
  Purchase #6 $212.49   9.625%   $232.9422   $232.94   $232.95   $232.90  
  Purchase #7 $40.93   3.366%   $42.3077   $42.31   $42.30   $42.30  
  7 purchase totals = $1,024.27       $1,124.1791   $1,124.17   $1,124.15   $1,124.20