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 $118.88   11.816%   $132.9269   $132.93   $132.95   $132.90  
  Purchase #2 $173.47   11.109%   $192.7408   $192.74   $192.75   $192.70  
  Purchase #3 $232.65   13.517%   $264.0973   $264.10   $264.10   $264.10  
  Purchase #4 $98.88   8.311%   $107.0979   $107.10   $107.10   $107.10  
  Purchase #5 $96.81   13.657%   $110.0313   $110.03   $110.05   $110.00  
  Purchase #6 $81.65   13.258%   $92.4752   $92.48   $92.50   $92.50  
  Purchase #7 $107.87   6.330%   $114.6982   $114.70   $114.70   $114.70  
  7 purchase totals = $910.21       $1,014.0676   $1,014.08   $1,014.15   $1,014.00