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 $200.78   4.269%   $209.3513   $209.35   $209.35   $209.40  
  Purchase #2 $220.81   10.199%   $243.3304   $243.33   $243.35   $243.30  
  Purchase #3 $147.67   13.262%   $167.254   $167.25   $167.25   $167.30  
  Purchase #4 $35.59   10.331%   $39.2668   $39.27   $39.25   $39.30  
  Purchase #5 $102.90   9.611%   $112.7897   $112.79   $112.80   $112.80  
  Purchase #6 $44.51   3.496%   $46.0661   $46.07   $46.05   $46.10  
  Purchase #7 $172.37   12.110%   $193.244   $193.24   $193.25   $193.20  
  7 purchase totals = $924.63       $1,011.3023   $1,011.30   $1,011.30   $1,011.40