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 $89.91   6.841%   $96.0607   $96.06   $96.05   $96.10  
  Purchase #2 $181.29   3.396%   $187.4466   $187.45   $187.45   $187.40  
  Purchase #3 $177.56   6.612%   $189.3003   $189.30   $189.30   $189.30  
  Purchase #4 $225.66   12.800%   $254.5445   $254.54   $254.55   $254.50  
  Purchase #5 $50.45   8.732%   $54.8553   $54.86   $54.85   $54.90  
  Purchase #6 $7.89   6.438%   $8.398   $8.40   $8.40   $8.40  
  Purchase #7 $219.99   5.635%   $232.3864   $232.39   $232.40   $232.40  
  7 purchase totals = $952.75       $1,022.9918   $1,023.00   $1,023.00   $1,023.00