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 $26.64   11.568%   $29.7217   $29.72   $29.70   $29.70  
  Purchase #2 $149.41   12.382%   $167.9099   $167.91   $167.90   $167.90  
  Purchase #3 $232.71   5.151%   $244.6969   $244.70   $244.70   $244.70  
  Purchase #4 $186.54   3.474%   $193.0204   $193.02   $193.00   $193.00  
  Purchase #5 $67.47   11.761%   $75.4051   $75.41   $75.40   $75.40  
  Purchase #6 $121.29   5.214%   $127.6141   $127.61   $127.60   $127.60  
  Purchase #7 $204.46   6.234%   $217.206   $217.21   $217.20   $217.20  
  7 purchase totals = $988.52       $1,055.5741   $1,055.58   $1,055.50   $1,055.50