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 $237.48   11.380%   $264.5052   $264.51   $264.50   $264.50  
  Purchase #2 $194.78   8.347%   $211.0383   $211.04   $211.05   $211.00  
  Purchase #3 $145.56   7.291%   $156.1728   $156.17   $156.15   $156.20  
  Purchase #4 $204.95   10.735%   $226.9514   $226.95   $226.95   $227.00  
  Purchase #5 $75.79   6.435%   $80.6671   $80.67   $80.65   $80.70  
  Purchase #6 $58.70   8.669%   $63.7887   $63.79   $63.80   $63.80  
  Purchase #7 $178.91   8.392%   $193.9241   $193.92   $193.90   $193.90  
  7 purchase totals = $1,096.17       $1,197.0476   $1,197.05   $1,197.00   $1,197.10