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 $183.97   7.676%   $198.0915   $198.09   $198.10   $198.10  
  Purchase #2 $51.68   7.391%   $55.4997   $55.50   $55.50   $55.50  
  Purchase #3 $225.39   10.394%   $248.817   $248.82   $248.80   $248.80  
  Purchase #4 $67.93   10.371%   $74.975   $74.98   $75.00   $75.00  
  Purchase #5 $124.70   4.494%   $130.304   $130.30   $130.30   $130.30  
  Purchase #6 $55.94   7.352%   $60.0527   $60.05   $60.05   $60.10  
  Purchase #7 $237.93   6.577%   $253.5787   $253.58   $253.60   $253.60  
  7 purchase totals = $947.54       $1,021.3186   $1,021.32   $1,021.35   $1,021.40