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 $186.27   13.592%   $211.5878   $211.59   $211.60   $211.60  
  Purchase #2 $119.71   3.751%   $124.2003   $124.20   $124.20   $124.20  
  Purchase #3 $20.73   10.776%   $22.9639   $22.96   $22.95   $23.00  
  Purchase #4 $200.53   12.702%   $226.0013   $226.00   $226.00   $226.00  
  Purchase #5 $183.90   8.626%   $199.7632   $199.76   $199.75   $199.80  
  Purchase #6 $165.67   11.118%   $184.0892   $184.09   $184.10   $184.10  
  Purchase #7 $45.50   7.371%   $48.8538   $48.85   $48.85   $48.90  
  7 purchase totals = $922.31       $1,017.4595   $1,017.45   $1,017.45   $1,017.60