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 $84.93   13.343%   $96.2622   $96.26   $96.25   $96.30  
  Purchase #2 $139.36   4.227%   $145.2507   $145.25   $145.25   $145.30  
  Purchase #3 $241.92   9.349%   $264.5371   $264.54   $264.55   $264.50  
  Purchase #4 $201.58   5.570%   $212.808   $212.81   $212.80   $212.80  
  Purchase #5 $53.79   13.113%   $60.8435   $60.84   $60.85   $60.80  
  Purchase #6 $166.33   8.188%   $179.9491   $179.95   $179.95   $179.90  
  Purchase #7 $249.51   7.597%   $268.4653   $268.47   $268.45   $268.50  
  7 purchase totals = $1,137.42       $1,228.1159   $1,228.12   $1,228.10   $1,228.10