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 $22.60   8.495%   $24.5199   $24.52   $24.50   $24.50  
  Purchase #2 $60.91   12.562%   $68.5615   $68.56   $68.55   $68.60  
  Purchase #3 $90.59   12.614%   $102.017   $102.02   $102.00   $102.00  
  Purchase #4 $128.85   10.441%   $142.3032   $142.30   $142.30   $142.30  
  Purchase #5 $167.94   4.479%   $175.462   $175.46   $175.45   $175.50  
  Purchase #6 $109.91   9.485%   $120.335   $120.34   $120.35   $120.30  
  Purchase #7 $39.44   9.615%   $43.2322   $43.23   $43.25   $43.20  
  7 purchase totals = $620.24       $676.4308   $676.43   $676.40   $676.40