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 $64.30   3.313%   $66.4303   $66.43   $66.45   $66.40  
  Purchase #2 $232.64   3.775%   $241.4222   $241.42   $241.40   $241.40  
  Purchase #3 $243.51   7.743%   $262.365   $262.37   $262.35   $262.40  
  Purchase #4 $175.68   11.455%   $195.8041   $195.80   $195.80   $195.80  
  Purchase #5 $46.94   5.119%   $49.3429   $49.34   $49.35   $49.30  
  Purchase #6 $135.34   6.110%   $143.6093   $143.61   $143.60   $143.60  
  Purchase #7 $213.61   4.418%   $223.0473   $223.05   $223.05   $223.00  
  7 purchase totals = $1,112.02       $1,182.0211   $1,182.02   $1,182.00   $1,181.90