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 $58.79   8.254%   $63.6425   $63.64   $63.65   $63.60  
  Purchase #2 $230.96   4.722%   $241.8659   $241.87   $241.85   $241.90  
  Purchase #3 $80.68   7.456%   $86.6955   $86.70   $86.70   $86.70  
  Purchase #4 $70.63   6.856%   $75.4724   $75.47   $75.45   $75.50  
  Purchase #5 $130.56   11.844%   $146.0235   $146.02   $146.00   $146.00  
  Purchase #6 $86.51   11.231%   $96.2259   $96.23   $96.25   $96.20  
  Purchase #7 $141.54   5.518%   $149.3502   $149.35   $149.35   $149.40  
  7 purchase totals = $799.67       $859.2759   $859.28   $859.25   $859.30