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 $46.74   13.472%   $53.0368   $53.04   $53.05   $53.00  
  Purchase #2 $123.68   12.393%   $139.0077   $139.01   $139.00   $139.00  
  Purchase #3 $95.45   7.649%   $102.751   $102.75   $102.75   $102.80  
  Purchase #4 $247.97   6.651%   $264.4625   $264.46   $264.45   $264.50  
  Purchase #5 $21.61   4.790%   $22.6451   $22.65   $22.65   $22.60  
  Purchase #6 $60.97   9.357%   $66.675   $66.68   $66.70   $66.70  
  Purchase #7 $219.48   7.148%   $235.1684   $235.17   $235.15   $235.20  
  7 purchase totals = $815.90       $883.7465   $883.76   $883.75   $883.80