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 $240.87   6.868%   $257.413   $257.41   $257.40   $257.40  
  Purchase #2 $54.61   12.620%   $61.5018   $61.50   $61.50   $61.50  
  Purchase #3 $114.30   6.309%   $121.5112   $121.51   $121.50   $121.50  
  Purchase #4 $87.49   9.655%   $95.9372   $95.94   $95.95   $95.90  
  Purchase #5 $147.95   11.829%   $165.451   $165.45   $165.45   $165.50  
  Purchase #6 $183.26   13.479%   $207.9616   $207.96   $207.95   $208.00  
  Purchase #7 $132.48   6.311%   $140.8408   $140.84   $140.85   $140.80  
  7 purchase totals = $960.96       $1,050.6166   $1,050.61   $1,050.60   $1,050.60