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 $247.37   8.186%   $267.6197   $267.62   $267.60   $267.60  
  Purchase #2 $123.94   8.417%   $134.372   $134.37   $134.35   $134.40  
  Purchase #3 $250.36   10.846%   $277.514   $277.51   $277.50   $277.50  
  Purchase #4 $58.30   6.409%   $62.0364   $62.04   $62.05   $62.00  
  Purchase #5 $123.85   9.465%   $135.5724   $135.57   $135.55   $135.60  
  Purchase #6 $73.30   11.401%   $81.6569   $81.66   $81.65   $81.70  
  Purchase #7 $75.97   11.579%   $84.7666   $84.77   $84.75   $84.80  
  7 purchase totals = $953.09       $1,043.5380   $1,043.54   $1,043.45   $1,043.60