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 $82.74   12.284%   $92.9038   $92.90   $92.90   $92.90  
  Purchase #2 $29.83   11.795%   $33.3484   $33.35   $33.35   $33.30  
  Purchase #3 $208.72   10.407%   $230.4415   $230.44   $230.45   $230.40  
  Purchase #4 $50.82   7.573%   $54.6686   $54.67   $54.65   $54.70  
  Purchase #5 $152.82   12.205%   $171.4717   $171.47   $171.45   $171.50  
  Purchase #6 $156.49   4.673%   $163.8028   $163.80   $163.80   $163.80  
  Purchase #7 $203.42   5.588%   $214.7871   $214.79   $214.80   $214.80  
  7 purchase totals = $884.84       $961.4239   $961.42   $961.40   $961.40