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 $77.44   12.836%   $87.3802   $87.38   $87.40   $87.40  
  Purchase #2 $26.56   3.524%   $27.496   $27.50   $27.50   $27.50  
  Purchase #3 $101.61   10.791%   $112.5747   $112.57   $112.55   $112.60  
  Purchase #4 $225.79   11.355%   $251.4285   $251.43   $251.45   $251.40  
  Purchase #5 $223.40   10.316%   $246.4459   $246.45   $246.45   $246.40  
  Purchase #6 $181.53   8.717%   $197.354   $197.35   $197.35   $197.40  
  Purchase #7 $126.71   5.787%   $134.0427   $134.04   $134.05   $134.00  
  7 purchase totals = $963.04       $1,056.7220   $1,056.72   $1,056.75   $1,056.70