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 $65.94   13.322%   $74.7245   $74.72   $74.70   $74.70  
  Purchase #2 $38.83   7.527%   $41.7527   $41.75   $41.75   $41.80  
  Purchase #3 $241.75   5.191%   $254.2992   $254.30   $254.30   $254.30  
  Purchase #4 $197.43   13.343%   $223.7731   $223.77   $223.75   $223.80  
  Purchase #5 $122.61   6.473%   $130.5465   $130.55   $130.55   $130.50  
  Purchase #6 $204.27   12.691%   $230.1939   $230.19   $230.20   $230.20  
  Purchase #7 $67.76   11.543%   $75.5815   $75.58   $75.60   $75.60  
  7 purchase totals = $938.59       $1,030.8714   $1,030.86   $1,030.85   $1,030.90