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 $46.27   6.601%   $49.3243   $49.32   $49.30   $49.30  
  Purchase #2 $167.71   11.126%   $186.3694   $186.37   $186.35   $186.40  
  Purchase #3 $243.67   10.353%   $268.8972   $268.90   $268.90   $268.90  
  Purchase #4 $243.53   12.666%   $274.3755   $274.38   $274.40   $274.40  
  Purchase #5 $225.81   11.250%   $251.2136   $251.21   $251.20   $251.20  
  Purchase #6 $196.31   7.651%   $211.3297   $211.33   $211.35   $211.30  
  Purchase #7 $35.95   10.352%   $39.6715   $39.67   $39.65   $39.70  
  7 purchase totals = $1,159.25       $1,281.1812   $1,281.18   $1,281.15   $1,281.20