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 $209.42   10.666%   $231.7567   $231.76   $231.75   $231.80  
  Purchase #2 $15.58   12.788%   $17.5724   $17.57   $17.55   $17.60  
  Purchase #3 $126.56   7.696%   $136.3001   $136.30   $136.30   $136.30  
  Purchase #4 $73.88   12.102%   $82.821   $82.82   $82.80   $82.80  
  Purchase #5 $231.91   12.224%   $260.2587   $260.26   $260.25   $260.30  
  Purchase #6 $134.56   6.772%   $143.6724   $143.67   $143.65   $143.70  
  Purchase #7 $191.98   6.689%   $204.8215   $204.82   $204.80   $204.80  
  7 purchase totals = $983.89       $1,077.2028   $1,077.20   $1,077.10   $1,077.30