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 $48.97   9.637%   $53.6892   $53.69   $53.70   $53.70  
  Purchase #2 $224.29   11.435%   $249.9376   $249.94   $249.95   $249.90  
  Purchase #3 $230.78   6.656%   $246.1407   $246.14   $246.15   $246.10  
  Purchase #4 $64.76   3.565%   $67.0687   $67.07   $67.05   $67.10  
  Purchase #5 $149.57   13.112%   $169.1816   $169.18   $169.20   $169.20  
  Purchase #6 $221.32   8.546%   $240.234   $240.23   $240.25   $240.20  
  Purchase #7 $10.39   11.367%   $11.571   $11.57   $11.55   $11.60  
  7 purchase totals = $950.08       $1,037.8228   $1,037.82   $1,037.85   $1,037.80