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 $244.94   13.217%   $277.3137   $277.31   $277.30   $277.30  
  Purchase #2 $208.42   12.585%   $234.6497   $234.65   $234.65   $234.60  
  Purchase #3 $212.87   11.505%   $237.3607   $237.36   $237.35   $237.40  
  Purchase #4 $57.70   7.115%   $61.8054   $61.81   $61.80   $61.80  
  Purchase #5 $39.73   8.694%   $43.1841   $43.18   $43.20   $43.20  
  Purchase #6 $179.81   9.331%   $196.5881   $196.59   $196.60   $196.60  
  Purchase #7 $45.78   3.289%   $47.2857   $47.29   $47.30   $47.30  
  7 purchase totals = $989.25       $1,098.1874   $1,098.19   $1,098.20   $1,098.20