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 $246.94   7.349%   $265.0876   $265.09   $265.10   $265.10  
  Purchase #2 $36.72   12.482%   $41.3034   $41.30   $41.30   $41.30  
  Purchase #3 $47.29   4.267%   $49.3079   $49.31   $49.30   $49.30  
  Purchase #4 $48.56   3.679%   $50.3465   $50.35   $50.35   $50.30  
  Purchase #5 $162.40   8.214%   $175.7395   $175.74   $175.75   $175.70  
  Purchase #6 $199.96   4.453%   $208.8642   $208.86   $208.85   $208.90  
  Purchase #7 $231.98   3.537%   $240.1851   $240.19   $240.20   $240.20  
  7 purchase totals = $973.85       $1,030.8342   $1,030.84   $1,030.85   $1,030.80