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 $52.92   7.586%   $56.9345   $56.93   $56.95   $56.90  
  Purchase #2 $119.91   5.593%   $126.6166   $126.62   $126.60   $126.60  
  Purchase #3 $44.33   7.797%   $47.7864   $47.79   $47.80   $47.80  
  Purchase #4 $155.58   3.183%   $160.5321   $160.53   $160.55   $160.50  
  Purchase #5 $172.36   8.219%   $186.5263   $186.53   $186.55   $186.50  
  Purchase #6 $41.30   12.142%   $46.3146   $46.31   $46.30   $46.30  
  Purchase #7 $161.48   5.534%   $170.4163   $170.42   $170.40   $170.40  
  7 purchase totals = $747.88       $795.1268   $795.13   $795.15   $795.00