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 $73.86   3.801%   $76.6674   $76.67   $76.65   $76.70  
  Purchase #2 $79.25   7.661%   $85.3213   $85.32   $85.30   $85.30  
  Purchase #3 $196.87   3.613%   $203.9829   $203.98   $204.00   $204.00  
  Purchase #4 $58.45   8.755%   $63.5673   $63.57   $63.55   $63.60  
  Purchase #5 $50.84   6.591%   $54.1909   $54.19   $54.20   $54.20  
  Purchase #6 $224.76   11.613%   $250.8614   $250.86   $250.85   $250.90  
  Purchase #7 $9.68   10.561%   $10.7023   $10.70   $10.70   $10.70  
  7 purchase totals = $693.71       $745.2935   $745.29   $745.25   $745.40