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 $92.44   13.124%   $104.5718   $104.57   $104.55   $104.60  
  Purchase #2 $160.35   9.367%   $175.37   $175.37   $175.35   $175.40  
  Purchase #3 $71.42   3.140%   $73.6626   $73.66   $73.65   $73.70  
  Purchase #4 $80.54   4.614%   $84.2561   $84.26   $84.25   $84.30  
  Purchase #5 $190.91   5.824%   $202.0286   $202.03   $202.05   $202.00  
  Purchase #6 $114.94   4.580%   $120.2043   $120.20   $120.20   $120.20  
  Purchase #7 $31.45   5.661%   $33.2304   $33.23   $33.25   $33.20  
  7 purchase totals = $742.05       $793.3238   $793.32   $793.30   $793.40