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 $192.39   10.148%   $211.9137   $211.91   $211.90   $211.90  
  Purchase #2 $237.77   13.278%   $269.3411   $269.34   $269.35   $269.30  
  Purchase #3 $36.49   9.266%   $39.8712   $39.87   $39.85   $39.90  
  Purchase #4 $60.50   11.569%   $67.4992   $67.50   $67.50   $67.50  
  Purchase #5 $10.58   11.523%   $11.7991   $11.80   $11.80   $11.80  
  Purchase #6 $13.79   6.183%   $14.6426   $14.64   $14.65   $14.60  
  Purchase #7 $241.77   9.497%   $264.7309   $264.73   $264.75   $264.70  
  7 purchase totals = $793.29       $879.7978   $879.79   $879.80   $879.70