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 $221.26   10.683%   $244.8972   $244.90   $244.90   $244.90  
  Purchase #2 $193.34   13.502%   $219.4448   $219.44   $219.45   $219.40  
  Purchase #3 $84.95   3.236%   $87.699   $87.70   $87.70   $87.70  
  Purchase #4 $182.69   11.317%   $203.365   $203.37   $203.35   $203.40  
  Purchase #5 $216.60   5.537%   $228.5931   $228.59   $228.60   $228.60  
  Purchase #6 $30.25   12.248%   $33.955   $33.96   $33.95   $34.00  
  Purchase #7 $229.39   10.747%   $254.0425   $254.04   $254.05   $254.00  
  7 purchase totals = $1,158.48       $1,271.9966   $1,272.00   $1,272.00   $1,272.00