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 $92.42   11.580%   $103.1222   $103.12   $103.10   $103.10  
  Purchase #2 $162.94   10.191%   $179.5452   $179.55   $179.55   $179.50  
  Purchase #3 $49.55   8.378%   $53.7013   $53.70   $53.70   $53.70  
  Purchase #4 $185.36   11.578%   $206.821   $206.82   $206.80   $206.80  
  Purchase #5 $88.54   13.514%   $100.5053   $100.51   $100.50   $100.50  
  Purchase #6 $118.61   5.626%   $125.283   $125.28   $125.30   $125.30  
  Purchase #7 $235.82   10.402%   $260.35   $260.35   $260.35   $260.40  
  7 purchase totals = $933.24       $1,029.3280   $1,029.33   $1,029.30   $1,029.30