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 $38.41   13.634%   $43.6468   $43.65   $43.65   $43.60  
  Purchase #2 $24.33   12.236%   $27.307   $27.31   $27.30   $27.30  
  Purchase #3 $91.38   12.656%   $102.9451   $102.95   $102.95   $102.90  
  Purchase #4 $132.99   4.523%   $139.0051   $139.01   $139.00   $139.00  
  Purchase #5 $137.84   8.559%   $149.6377   $149.64   $149.65   $149.60  
  Purchase #6 $148.76   12.695%   $167.6451   $167.65   $167.65   $167.60  
  Purchase #7 $134.39   3.274%   $138.7899   $138.79   $138.80   $138.80  
  7 purchase totals = $708.10       $768.9767   $769.00   $769.00   $768.80