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 $229.28   8.489%   $248.7436   $248.74   $248.75   $248.70  
  Purchase #2 $220.95   9.810%   $242.6252   $242.63   $242.65   $242.60  
  Purchase #3 $191.88   7.321%   $205.9275   $205.93   $205.95   $205.90  
  Purchase #4 $37.72   6.199%   $40.0583   $40.06   $40.05   $40.10  
  Purchase #5 $182.61   10.539%   $201.8553   $201.86   $201.85   $201.90  
  Purchase #6 $5.31   11.542%   $5.9229   $5.92   $5.90   $5.90  
  Purchase #7 $80.46   9.399%   $88.0224   $88.02   $88.00   $88.00  
  7 purchase totals = $948.21       $1,033.1552   $1,033.16   $1,033.15   $1,033.10