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 $183.35   9.647%   $201.0378   $201.04   $201.05   $201.00  
  Purchase #2 $85.96   6.358%   $91.4253   $91.43   $91.45   $91.40  
  Purchase #3 $235.56   11.566%   $262.8049   $262.80   $262.80   $262.80  
  Purchase #4 $65.71   13.510%   $74.5874   $74.59   $74.60   $74.60  
  Purchase #5 $108.37   6.386%   $115.2905   $115.29   $115.30   $115.30  
  Purchase #6 $60.26   13.634%   $68.4758   $68.48   $68.50   $68.50  
  Purchase #7 $210.25   5.601%   $222.0261   $222.03   $222.05   $222.00  
  7 purchase totals = $949.46       $1,035.6478   $1,035.66   $1,035.75   $1,035.60