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 $101.95   10.567%   $112.7231   $112.72   $112.70   $112.70  
  Purchase #2 $29.92   12.450%   $33.645   $33.65   $33.65   $33.60  
  Purchase #3 $80.58   5.424%   $84.9507   $84.95   $84.95   $85.00  
  Purchase #4 $180.29   13.116%   $203.9368   $203.94   $203.95   $203.90  
  Purchase #5 $98.49   9.802%   $108.144   $108.14   $108.15   $108.10  
  Purchase #6 $191.99   11.815%   $214.6736   $214.67   $214.65   $214.70  
  Purchase #7 $194.43   4.191%   $202.5786   $202.58   $202.60   $202.60  
  7 purchase totals = $877.65       $960.6518   $960.65   $960.65   $960.60