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 $152.50   7.749%   $164.3172   $164.32   $164.30   $164.30  
  Purchase #2 $211.42   13.348%   $239.6403   $239.64   $239.65   $239.60  
  Purchase #3 $20.86   7.253%   $22.373   $22.37   $22.35   $22.40  
  Purchase #4 $129.57   12.268%   $145.4656   $145.47   $145.45   $145.50  
  Purchase #5 $135.86   6.685%   $144.9422   $144.94   $144.95   $144.90  
  Purchase #6 $25.57   5.270%   $26.9175   $26.92   $26.90   $26.90  
  Purchase #7 $118.90   6.233%   $126.311   $126.31   $126.30   $126.30  
  7 purchase totals = $794.68       $869.9668   $869.97   $869.90   $869.90