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 $45.88   3.709%   $47.5817   $47.58   $47.60   $47.60  
  Purchase #2 $165.51   6.363%   $176.0414   $176.04   $176.05   $176.00  
  Purchase #3 $220.96   8.810%   $240.4266   $240.43   $240.45   $240.40  
  Purchase #4 $209.89   10.817%   $232.5938   $232.59   $232.60   $232.60  
  Purchase #5 $187.62   3.412%   $194.0216   $194.02   $194.00   $194.00  
  Purchase #6 $37.63   8.541%   $40.844   $40.84   $40.85   $40.80  
  Purchase #7 $156.91   9.681%   $172.1005   $172.10   $172.10   $172.10  
  7 purchase totals = $1,024.40       $1,103.6096   $1,103.60   $1,103.65   $1,103.50