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 $184.29   13.220%   $208.6531   $208.65   $208.65   $208.70  
  Purchase #2 $143.35   4.519%   $149.828   $149.83   $149.85   $149.80  
  Purchase #3 $141.60   7.315%   $151.958   $151.96   $151.95   $152.00  
  Purchase #4 $53.51   13.250%   $60.6001   $60.60   $60.60   $60.60  
  Purchase #5 $179.50   4.357%   $187.3208   $187.32   $187.30   $187.30  
  Purchase #6 $236.57   3.573%   $245.0226   $245.02   $245.00   $245.00  
  Purchase #7 $217.93   6.291%   $231.64   $231.64   $231.65   $231.60  
  7 purchase totals = $1,156.75       $1,235.0226   $1,235.02   $1,235.00   $1,235.00