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 $92.42   6.368%   $98.3053   $98.31   $98.30   $98.30  
  Purchase #2 $237.97   11.789%   $266.0243   $266.02   $266.00   $266.00  
  Purchase #3 $138.83   7.860%   $149.742   $149.74   $149.75   $149.70  
  Purchase #4 $80.54   3.574%   $83.4185   $83.42   $83.40   $83.40  
  Purchase #5 $76.59   4.442%   $79.9921   $79.99   $80.00   $80.00  
  Purchase #6 $237.98   5.700%   $251.5449   $251.54   $251.55   $251.50  
  Purchase #7 $114.34   3.705%   $118.5763   $118.58   $118.60   $118.60  
  7 purchase totals = $978.67       $1,047.6034   $1,047.60   $1,047.60   $1,047.50