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 $77.57   7.746%   $83.5786   $83.58   $83.60   $83.60  
  Purchase #2 $201.32   5.189%   $211.7665   $211.77   $211.75   $211.80  
  Purchase #3 $173.26   11.634%   $193.4171   $193.42   $193.40   $193.40  
  Purchase #4 $11.76   9.621%   $12.8914   $12.89   $12.90   $12.90  
  Purchase #5 $41.63   3.779%   $43.2032   $43.20   $43.20   $43.20  
  Purchase #6 $223.65   13.628%   $254.129   $254.13   $254.15   $254.10  
  Purchase #7 $212.34   9.607%   $232.7395   $232.74   $232.75   $232.70  
  7 purchase totals = $941.53       $1,031.7253   $1,031.73   $1,031.75   $1,031.70