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 $86.70   10.796%   $96.0601   $96.06   $96.05   $96.10  
  Purchase #2 $187.85   13.683%   $213.5535   $213.55   $213.55   $213.60  
  Purchase #3 $75.84   6.726%   $80.941   $80.94   $80.95   $80.90  
  Purchase #4 $245.81   12.173%   $275.7325   $275.73   $275.75   $275.70  
  Purchase #5 $246.25   7.738%   $265.3048   $265.30   $265.30   $265.30  
  Purchase #6 $92.35   10.764%   $102.2906   $102.29   $102.30   $102.30  
  Purchase #7 $90.90   5.651%   $96.0368   $96.04   $96.05   $96.00  
  7 purchase totals = $1,025.70       $1,129.9193   $1,129.91   $1,129.95   $1,129.90