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 $200.51   11.218%   $223.0032   $223.00   $223.00   $223.00  
  Purchase #2 $247.96   11.589%   $276.6961   $276.70   $276.70   $276.70  
  Purchase #3 $214.57   6.649%   $228.8368   $228.84   $228.85   $228.80  
  Purchase #4 $153.64   4.469%   $160.5062   $160.51   $160.50   $160.50  
  Purchase #5 $65.60   4.755%   $68.7193   $68.72   $68.70   $68.70  
  Purchase #6 $218.39   5.579%   $230.574   $230.57   $230.55   $230.60  
  Purchase #7 $246.33   10.255%   $271.5911   $271.59   $271.60   $271.60  
  7 purchase totals = $1,347.00       $1,459.9267   $1,459.93   $1,459.90   $1,459.90