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 $248.79   6.238%   $264.3095   $264.31   $264.30   $264.30  
  Purchase #2 $110.60   5.720%   $116.9263   $116.93   $116.95   $116.90  
  Purchase #3 $125.27   9.812%   $137.5615   $137.56   $137.55   $137.60  
  Purchase #4 $245.27   9.855%   $269.4414   $269.44   $269.45   $269.40  
  Purchase #5 $80.79   5.268%   $85.046   $85.05   $85.05   $85.00  
  Purchase #6 $71.26   5.831%   $75.4152   $75.42   $75.40   $75.40  
  Purchase #7 $91.71   5.439%   $96.6981   $96.70   $96.70   $96.70  
  7 purchase totals = $973.69       $1,045.3980   $1,045.41   $1,045.40   $1,045.30