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 $51.42   9.206%   $56.1537   $56.15   $56.15   $56.20  
  Purchase #2 $246.68   8.731%   $268.2176   $268.22   $268.20   $268.20  
  Purchase #3 $205.34   6.386%   $218.453   $218.45   $218.45   $218.50  
  Purchase #4 $111.53   8.812%   $121.358   $121.36   $121.35   $121.40  
  Purchase #5 $97.73   11.636%   $109.1019   $109.10   $109.10   $109.10  
  Purchase #6 $50.70   10.561%   $56.0544   $56.05   $56.05   $56.10  
  Purchase #7 $105.30   6.573%   $112.2214   $112.22   $112.20   $112.20  
  7 purchase totals = $868.70       $941.5600   $941.55   $941.50   $941.70