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 $114.97   7.260%   $123.3168   $123.32   $123.30   $123.30  
  Purchase #2 $186.58   5.365%   $196.59   $196.59   $196.60   $196.60  
  Purchase #3 $162.69   4.544%   $170.0826   $170.08   $170.10   $170.10  
  Purchase #4 $197.69   6.796%   $211.125   $211.13   $211.15   $211.10  
  Purchase #5 $96.73   11.241%   $107.6034   $107.60   $107.60   $107.60  
  Purchase #6 $238.75   6.179%   $253.5024   $253.50   $253.50   $253.50  
  Purchase #7 $72.78   3.317%   $75.1941   $75.19   $75.20   $75.20  
  7 purchase totals = $1,070.19       $1,137.4143   $1,137.41   $1,137.45   $1,137.40