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 $207.57   5.507%   $219.0009   $219.00   $219.00   $219.00  
  Purchase #2 $144.82   12.849%   $163.4279   $163.43   $163.45   $163.40  
  Purchase #3 $148.99   12.521%   $167.645   $167.65   $167.65   $167.60  
  Purchase #4 $167.32   5.158%   $175.9504   $175.95   $175.95   $176.00  
  Purchase #5 $13.75   12.586%   $15.4806   $15.48   $15.50   $15.50  
  Purchase #6 $158.80   12.672%   $178.9231   $178.92   $178.90   $178.90  
  Purchase #7 $85.39   13.280%   $96.7298   $96.73   $96.75   $96.70  
  7 purchase totals = $926.64       $1,017.1577   $1,017.16   $1,017.20   $1,017.10