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 $193.29   5.829%   $204.5569   $204.56   $204.55   $204.60  
  Purchase #2 $239.26   6.311%   $254.3597   $254.36   $254.35   $254.40  
  Purchase #3 $152.54   9.408%   $166.891   $166.89   $166.90   $166.90  
  Purchase #4 $105.92   10.735%   $117.2905   $117.29   $117.30   $117.30  
  Purchase #5 $230.29   4.805%   $241.3554   $241.36   $241.35   $241.40  
  Purchase #6 $85.75   12.570%   $96.5288   $96.53   $96.55   $96.50  
  Purchase #7 $111.67   9.755%   $122.5634   $122.56   $122.55   $122.60  
  7 purchase totals = $1,118.72       $1,203.5457   $1,203.55   $1,203.55   $1,203.70