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 $160.58   13.279%   $181.9034   $181.90   $181.90   $181.90  
  Purchase #2 $68.84   11.361%   $76.6609   $76.66   $76.65   $76.70  
  Purchase #3 $194.27   4.593%   $203.1928   $203.19   $203.20   $203.20  
  Purchase #4 $246.98   3.247%   $254.9994   $255.00   $255.00   $255.00  
  Purchase #5 $179.37   5.168%   $188.6398   $188.64   $188.65   $188.60  
  Purchase #6 $127.64   13.296%   $144.611   $144.61   $144.60   $144.60  
  Purchase #7 $24.81   4.159%   $25.8418   $25.84   $25.85   $25.80  
  7 purchase totals = $1,002.49       $1,075.8491   $1,075.84   $1,075.85   $1,075.80