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 $32.35   12.873%   $36.5144   $36.51   $36.50   $36.50  
  Purchase #2 $179.35   8.127%   $193.9258   $193.93   $193.95   $193.90  
  Purchase #3 $236.68   12.594%   $266.4875   $266.49   $266.50   $266.50  
  Purchase #4 $171.52   13.864%   $195.2995   $195.30   $195.30   $195.30  
  Purchase #5 $80.90   11.689%   $90.3564   $90.36   $90.35   $90.40  
  Purchase #6 $88.43   11.747%   $98.8179   $98.82   $98.80   $98.80  
  Purchase #7 $207.48   6.478%   $220.9206   $220.92   $220.90   $220.90  
  7 purchase totals = $996.71       $1,102.3221   $1,102.33   $1,102.30   $1,102.30