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 $78.55   13.116%   $88.8526   $88.85   $88.85   $88.90  
  Purchase #2 $192.50   5.152%   $202.4176   $202.42   $202.40   $202.40  
  Purchase #3 $210.36   10.338%   $232.107   $232.11   $232.10   $232.10  
  Purchase #4 $34.48   9.565%   $37.778   $37.78   $37.80   $37.80  
  Purchase #5 $93.53   13.168%   $105.846   $105.85   $105.85   $105.80  
  Purchase #6 $184.40   12.654%   $207.734   $207.73   $207.75   $207.70  
  Purchase #7 $19.96   11.123%   $22.1802   $22.18   $22.20   $22.20  
  7 purchase totals = $813.78       $896.9154   $896.92   $896.95   $896.90