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 $126.59   10.331%   $139.668   $139.67   $139.65   $139.70  
  Purchase #2 $163.79   9.759%   $179.7743   $179.77   $179.75   $179.80  
  Purchase #3 $91.39   4.662%   $95.6506   $95.65   $95.65   $95.70  
  Purchase #4 $36.56   13.232%   $41.3976   $41.40   $41.40   $41.40  
  Purchase #5 $246.67   7.375%   $264.8619   $264.86   $264.85   $264.90  
  Purchase #6 $240.44   7.489%   $258.4466   $258.45   $258.45   $258.40  
  Purchase #7 $33.78   3.693%   $35.0275   $35.03   $35.05   $35.00  
  7 purchase totals = $939.22       $1,014.8265   $1,014.83   $1,014.80   $1,014.90