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 $238.37   5.514%   $251.5137   $251.51   $251.50   $251.50  
  Purchase #2 $215.61   13.513%   $244.7454   $244.75   $244.75   $244.70  
  Purchase #3 $37.30   10.483%   $41.2102   $41.21   $41.20   $41.20  
  Purchase #4 $87.94   6.411%   $93.5778   $93.58   $93.60   $93.60  
  Purchase #5 $168.98   7.270%   $181.2648   $181.26   $181.25   $181.30  
  Purchase #6 $250.90   5.396%   $264.4386   $264.44   $264.45   $264.40  
  Purchase #7 $59.54   3.270%   $61.487   $61.49   $61.50   $61.50  
  7 purchase totals = $1,058.64       $1,138.2375   $1,138.24   $1,138.25   $1,138.20