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 $216.48   3.376%   $223.7884   $223.79   $223.80   $223.80  
  Purchase #2 $219.92   4.102%   $228.9411   $228.94   $228.95   $228.90  
  Purchase #3 $19.98   12.780%   $22.5334   $22.53   $22.55   $22.50  
  Purchase #4 $136.64   6.293%   $145.2388   $145.24   $145.25   $145.20  
  Purchase #5 $246.90   11.503%   $275.3009   $275.30   $275.30   $275.30  
  Purchase #6 $32.84   3.524%   $33.9973   $34.00   $34.00   $34.00  
  Purchase #7 $226.59   12.757%   $255.4961   $255.50   $255.50   $255.50  
  7 purchase totals = $1,099.35       $1,185.2960   $1,185.30   $1,185.35   $1,185.20