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 $236.49   13.808%   $269.1445   $269.14   $269.15   $269.10  
  Purchase #2 $167.75   9.615%   $183.8792   $183.88   $183.90   $183.90  
  Purchase #3 $160.38   13.342%   $181.7779   $181.78   $181.80   $181.80  
  Purchase #4 $207.87   6.104%   $220.5584   $220.56   $220.55   $220.60  
  Purchase #5 $119.49   4.744%   $125.1586   $125.16   $125.15   $125.20  
  Purchase #6 $50.67   12.146%   $56.8244   $56.82   $56.80   $56.80  
  Purchase #7 $98.98   11.419%   $110.2825   $110.28   $110.30   $110.30  
  7 purchase totals = $1,041.63       $1,147.6255   $1,147.62   $1,147.65   $1,147.70