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 $53.67   8.104%   $58.0194   $58.02   $58.00   $58.00  
  Purchase #2 $23.95   11.253%   $26.6451   $26.65   $26.65   $26.60  
  Purchase #3 $6.96   11.853%   $7.785   $7.79   $7.80   $7.80  
  Purchase #4 $220.30   11.835%   $246.3725   $246.37   $246.35   $246.40  
  Purchase #5 $107.59   5.407%   $113.4074   $113.41   $113.40   $113.40  
  Purchase #6 $117.59   12.231%   $131.9724   $131.97   $131.95   $132.00  
  Purchase #7 $100.53   7.245%   $107.8134   $107.81   $107.80   $107.80  
  7 purchase totals = $630.59       $692.0152   $692.02   $691.95   $692.00